Erm, I didnt really find any of it HARD as such - the "Follow the line using the two joysticks" was a little painful, I'm used to having the sticks reversed to the way they had them! (Also, if you hold the sticks LOWER down the joystick, it makes the joystick FAR less twitchy! I rested my hands each side of the sticks, and held the sticks at that height, rather than hands "hovering" and trying to hold the sticks.)
When I got the email for the training centre tests - it came with some test papers, I ran through all of those twice.
On the day, just go for speed AND accuracy - but Accuracy over all. The tests and timing, making you leave stuff unfinished etc - I believe is to put you under stress and see how you perform.
I was more worried about the MMI (Multi Modal Interview) - turns out that was the best part of the process

Just answer the 6 questions honestly, and give accurate answers to questions - I used the same answer for 2 questions. The short computer test before the MMI helps the system come up with relevant questions TO YOU, which they will use to "top up" your answers if needed.
There was a single safety question, along the lines of "A colleague tells you you can skip over a safety step in the shift start train checks, What do you do?"
Turns out quite a few people say "Skip it"...... and thats where their interview ends! (Its a safety step, FOR A REASON!)
Get a decent nights sleep, get there 30 mins early, sign in. make yourself a drink and calm down
GOOD LUCK