Oh, I'm sure I've got a few...
Rail fares should always be less than the cost of driving. (Note: the cost of driving === the cost of the fuel used for the journey. This shouldn't need saying, since it is dead obvious when you actually do the journey and look at what you actually spend, but unfortunately far too many people insist on arguing otherwise by spuriously including money you spend at other times, which is irrelevant; pretending you pay twice for buying the car in the first place and adding a portion of that on as well, which is silly; and other made-up accountants' rubbish which does not exist in the real world. People who make such arguments should be nailed to the sleepers and left there for a week.) The cost of a rail fare should be calculated by measuring the great-circle distance from A to B, calculating how much the petrol/diesel would cost to cover that distance according to the average of the mpg of the most frugal cars from the top five manufacturers (or something along those lines, you get the idea), and then knocking 10% off for luck.
The fare calculated by the above method is to be the only fare for the journey. Stuff all this nonsense of booking in advance, different fares at different times of day, and all that. Variation in demand with time should be handled by increasing the length/frequency of trains at times of high demand. (Yes, this means that the stock will be sitting in sidings at times of low demand. No, this doesn't matter. It does not cost money to not run stock, it only costs money when it's accumulating miles. Accountants' arguments to the contrary are based on an inability to tell the difference between zero and a negative number, and on making up costs that don't exist; anyone making such arguments should be nailed to the sleepers and left there for a week.)
Railways should not be operated to make a profit, any more than roads are. They should be paid for out of the general tax pot, like the roads are. (Note: car tax, fuel tax etc. do not go into a separate "roads" pot, they go into the same general pot as everything else.)
Graffiti on trains should be encouraged because it saves the railways having to paint the trains themselves. (Just make sure that it doesn't cover the windows.)
A team of botanists should be tasked with finding plants that improve the characteristics of ballast, and make it last longer, by growing in it, and weed removal should be followed by sowing these plants. This will both reduce the need for track maintenance, and make stations much more pleasant places to wait on because green growing things are so much nicer than arid barren stone and concrete.
All trains should have smoking accommodation. People who don't like smoking can sit in the non-smoking bit like they always used to. And stop prohibiting it on stations, too, it's in the open air for crying out loud.
All routes should be maintained and signalled for the maximum line speed that is possible given the curvature of the formation. No more of this nonsense of trundling along some piece of dead straight track for miles and miles at the speed of continental drift because they can't be bothered to maintain it any better. Junctions and pointwork should be upgraded so they can be traversed without slowing down (within above curvature limits). On major routes any curvature that dictates a speed below 100mph should be eased until that is no longer the case.
At the other end of the scale, line speeds higher than 125mph are pointless. This is a little country, and 125mph is buckets... as long as you can actually maintain it and don't have to keep slowing down for things that have been skimped.
As for HS2, it is a moronic idea. The speed is pointless, making it ridiculously expensive and preventing its use by normal traffic, and it misses out nearly everywhere. Scrap it, and instead do things like building a four-track main line for conventional speeds that actually goes to places and connects with existing routes and can carry freight, reversing the damage to capacity caused by years of "track irrationalisation", lengthening platforms and running longer trains, providing plenty of crossovers for fasts to overtake stoppers, building flyovers/diveunders to eliminate conflicts... recognising that we've already got 3 routes from London to Birmingham that do go to places and it's daft to build a brand new one because we're too dumb to use them properly, that we've already got an underused four-track main line (that's had its capacity massacred) to much of the populous north plus the trackbed of another route, that the energy use for a given journey rises with the square of the speed and the required traction power with the cube, that by far the more effective means to increase average speed is not to raise the peaks in the speed/time curve but to fill in the troughs, etc. etc. etc.
Selling off railway land should be banned. Land that has already been sold off should have all construction on it prohibited. Anything that has been built on it already is to be demolished as soon as the current occupants move out. Any road or cycle path that it's been used for is to be regarded as occupying it only by grace and favour and it's up to the people who put it there to find an alternative route if the railway is reopened.
Safety should operate on "Darwin rules". People should be allowed to be stupid and should not be allowed to blame the consequences on others. If you stick your head out the window and do a Vyvyan, or touch the live rail, or walk out of a train door when it's not at a platform and fall into a canal, etc, etc, then fine, if that's what you like doing, but you can't sue the railways for it and the railways don't have to try and stop you.
Electrification is overrated. The total conversion efficiency from raw fuel to tractive power is about the same whether the generating plant is remote or on-board, and insisting on electrification of reopened lines just tends to mean they don't get reopened at all. People who have, in the past couple of years, suddenly discovered the pastime of getting all hysterical about diesel fumes even though the actual pollution levels are lower than ever before in their lifetimes, should be nailed to the sleepers and left there for a week. Not saying it shouldn't be done, but that apart from filling in obvious silly gaps it shouldn't take precedence over other things or be the reason they're not done at all.
Similarly, 25kV overhead is overrated. It looks flaming awful, it causes problems with finding overhead clearance for it, it tends to have catastrophic failure modes that take out an entire route rather than just one track, it's up in the air so even trivial maintenance is a palaver. Instead we should be using something like four-rail DC at +/-1.5kV with the rails linked to large-section aluminium distribution bus bars every 100m or so - this kind of method gets the losses down to the same level as 25kV achieves. Live rails aren't actually any more dangerous to rail staff than overhead, according to accident figures. They may be more dangerous to trespassers but that's their own fault for being where they shouldn't in the first place, see above re. Darwin rules. The higher voltage is not higher enough to change the nature of the danger it presents. The use of DC does not preclude regenerative braking that returns power to the grid (as long as you don't insist on using substation technology that dates back to mercury-arc rectifiers and ignoring the capabilities of modern power semiconductors). Clearance becomes a trivial matter and maintenance is as straightforward as with anything else at ground level.
Drivers should drive the train not from the front, but from the rear, using a high definition video link. This is to avoid situations like Ladboke Grove or Moorgate, where you have a screaming need to ask the driver "just what in the name of alien duck sex did you think you were doing?", but you can't. It also means that passengers can sit in the front instead and look out, as was possible with old DMUs. (And the video signal should also be made available over the internet, if the train has an uplink already.)
Air conditioning is not necessary in Britain. In the winter, ordinary heating is needed, and this is much less likely to go wrong. In the summer, open the flipping windows ffs. (And, of course, make them openable - and openable properly, too, without trying to make them so people can't stick their head out and making it so they don't let any air in either, see above re. Darwin.)
Multiple units should be confined to the HST pattern, with traction equipment and passenger accommodation in separate vehicles. And if the traction equipment fails the traction vehicle can be removed and replaced with another one, after which the train continues on its journey.
If you must have electronic destination displays in the carriages, make them static and passive: use an "e-ink" panel or something which is large enough to get all the text on at once, and keep it still. NOT glaring flashing scrolling mega-bright orange LEDs that you can't ignore even if you want to because they're a bright moving object in your visual field.
Bringing bicycles on trains should not be discouraged. A huge problem with trains is that while you have your car or bicycle to get to the station at the "home" end of the journey, at the "away" end you haven't and it's probably an outrageously long walk to where you actually want to be. Even I can't see it being practical to take your car on the train, but a bicycle is another matter, and it goes a long long way towards mitigating the problem. Lifts on stations should be big enough to get a bicycle in and should not require a member of staff to operate them, and in the absence of lifts you should be able to take the bicycle across the board crossing; having to struggle carrying the thing up the stairs is not on.
All trains should have at least one vehicle for "awkward loads". Like the bicycles. Like a guard's van, but nicer inside so people in wheelchairs can ride in it as well. It has a power-operated ramp fitted to the doors to get them in and out with, and it has the enormous toilet with the door that comes open on you when you're half way through doing your business so the rest of the train can have normal toilets with proper doors. And it has a couple of seats for blind people with loudspeakers in them so the rest of the train doesn't have the flaming things constantly yapping at you on and on and on.
The Crudworth route should be reinstated, because it is an insult to the memory of the Midland Railway to have that gap in an otherwise continuous route. And then we should have a St Pancras - Nottingham - Glasgow service over it.
Holborn Viaduct station and the missing bridge at Blackfriars should be reinstated to help with capacity in that area. And Cannon Street station should have its original roof rebuilt, because the way it is at the moment it looks like a UFO is taking a dump in it.
No stock which does not have all seating bays aligned with windows should be passed for service.
Seat designers who proudly produce diagrams to show how great their designs are which feature those ridiculous outline human figures all sitting rigidly "to attention" like deactivated Autons for a three-hour journey should be nailed to the sleepers and left there for a week. Seating layout designers who do not consider that people have legs should have their own legs cut off. (I am a few inches below average height, before anyone asks.)
There should be an end to the practice of cluttering up the concourses of terminal stations with portakabins containing crappy shops selling small amounts of crappy food at outrageous prices, and then keeping the barriers closed until the train's about to leave so people can't wait on the platforms but are forced to wait near the shops in the hope that it'll make them buy stuff. It's crowded and stuffy and sticky and the shops blow out gusts of hot smelly air and it does my head in. I want some space, and I'm not going to buy anything that's such a rip-off. Get rid of the 10 different variations of "spend five quid on things with silly names and still be hungry" and just have one buffet selling normal food with the same price/quantity ratio as a chip shop and who understand simple straightforward requests like "a cup of coffee, please". As for the shops selling stupid things like neckties, this is a railway station ffs, just lose them altogether. And open the barriers already.
What they've done to St Pancras station is an abomination. There's a thing like a petrol station glued onto the end of the Barlow trainshed which makes it look ridiculous. All the terminating trains for normal people use only the petrol station, so you're waiting for your train in this horrible soulless petrol station thing which is even harder and more unwelcoming than Euston. You don't get to use the proper trainshed because it's all walled off for Eurostar, which should have stayed at Waterloo. They've cut dirty great holes in the deck, which compromises the structure because the deck is supposed to be in tension tying the bottom ends of the roof arches together, and filled the place with horrible crappy shops as if it wasn't in a whole enormous city full of horrible crappy shops already. It's all glitzy and commercially oppressive and the atmosphere is completely gone. The calm spacious grandeur of that huge empty airy trainshed with the simplicity of the long parallel bare platforms is ruined. They might as well rename it The Arndale Centre. And on top of all that it's such a flaming long way from the petrol station to the Underground that it needs a branch built and a shuttle service run between the two.
When it comes to reopening a line they should just get on with it and flipping well do it. By the time they've messed around for ten years paying hundreds of millions of pounds to "consultants" to produce glossy bookets full of made-up figures supporting the conclusion they were told to make them support, they could have got the line reopened by now for the same cost, whereas instead during all the time they've spent messing about the cost has gone up so much that they can't do it any more and have to go round the same idiotic merry-go-round again, repeat ad nauseam. If the Victorians could go from having the idea to having a complete brand new railway in less than five years, doing it all by hand, then with modern machinery we ought to be able to do it in half that time at the outside.
They should join the Waterloo & City line to Moorgate just to confuse all the people who will see a dead short straight line on the Underground map and then wonder why it feels like a roller coaster to ride on and takes 10 minutes.