Kitchen units aren't that hard to fit the a few but if advice that I've learnt from during ours:
IKEA units have no gaps at the back unlike most others. This was fine for us as the plumbing was contained behind one unit so limited need for cutting out of back panels. However could be a right pain in some kitchens. However this does mean you get deeper cupboards.
IKEA site you to fit wall cupboards as base cupboards, this was useful for us as it allows a row of cupboards next to our table whilst giving people at the take about 10cm each of extra space. This means that people can just get past someone sat down, which makes the space a lot better.
IKEA have some worktops that are custom orders, this means that they cut them for you and ask you have to do is bolt them together. It means that you pay more for the worktops but save on the fitting costs. You still need to cut the hole for the sink, which requires a jigsaw, but make sure it's a good one as otherwise it will take an age to do.
Make sure you fit your worktop for the sink with a slight fall so that it drains well.
When fitting units fit a temporary batton asking the underside of where the units will run. This allows you to get that level a lot more easier that the units, it also allows you to test the units on it whilst you fit them. It is such a big benefit that it more than offsets the costs of the few bits of wood and several screws and wall plugs you'll use. Given that most people will rule or for splashbacks any holes are covered up anyway.
Laminate flooring is easy to fit, when we did ours B&Q did a slate looking one that looks very real, to the extent that wires a few people thought that it was real slate. Fit insulation under it.
If you know someone with a water cooled the cutter ask to borrow it as it will make cutting tiles a breeze. We rarely broke or miss cut tiles when we used one.
Make sure that you allow for about 10% more flooring, tiles, etc. As there will be left over short bus that you can't use, those that get miss cut, those that break, etc. As you don't want to have to go back halfway through a project.
Check with work to see if you have any company benefits that get you discounts anywhere, if not find an older relative who can get 10% off with a diamond card at B&Q.
Shop around, you may still find it cheaper at the likes of screwfix than at Wikes or B&Q even with discounts.
Try and make space for a dishwasher (even if you fit a cupboard in that space to start with).
Freestanding cookers are cheaper, but depending on your layout built in can be better (just try and avoid putting it so it causes dark corners).
If you need double glazing, arrange the appointment with their sales staff before you move in. It means that they don't hang around as they have to stand up! This means that they cut to the chase a lot quicker and avoids all that sales play.
Another truck is to arrange for three at once and tell them all that you'll go with the cheapest and leave them to fight it out (bit that I've done this, but I did do the before moving in).
With all trades be willing to be cheaky and ask for extras (i.e. while your doing X could you do Y as well...) espcilay if the extras are a little fiddly. As an example, whilst getting a boiler serviced ask about plumbing in the kitchen sink, you may only be charged for parts.