OK this may seem harsh what I am about to say but please take it constructively.
The key to the best shots is location. That is the problem with a number of your shots.
1. This is not a bad location but you are there at the wrong time of day. You can see that the sun is illuminating the cutting where the wagons are at the rear of the train. I would guess this is taken at either the beginning or the end of the day when the bottom of the cutting is in shade. This location may work with the sun in a different location at a different time of day.
2. This looks like it was taken at dusk. It is very difficult to get a good shot at this time of the day. The location is not great. You are too side on and the power lines also look to be going across the picture. You need to look what else is in the picture, not just the train.
3. Nice try. You need the sun on this side. This could have worked at a different time of day.
4. Either too slow a shutter speed or out of focus, can't tell. You also have too much clutter in the left of the photo. Station signage etc. This takes a little while to master.
5. Is not bad. Shutter pressed slightly too early but this could be recovered by a tighter crop of the picture.
6. I don't think you could have done better.
As for location anywhere can work but look at the whole picture you are taking.
Another tip, look at a good quality image site like
www.railpictures.net. You can filter by country if you are only interested in the UK. See what you like and how the picture has been taken. Try to replicate what you like.
Hope this is not too critical and provides you useful advice.
Some of my stuff is below.