Angry_Muppet
Had my tests last Friday and despite knowing I'd missed or answered incorrectly a lot, especially on the number sorting and maths questions whilst avoiding collisions tests, I still passed and have my Stage 3 next month.
I'd suggest finding something to help you practice using the number keypad with one hand whilst choosing one of four options with your other hand at the same time. This can be as simple getting a friend to shout out random sequences while you press away without taking your eyes off the screen.
And you're right about the main problem being overcoming your mistakes. Stay relaxed and focussed and concentrate on the current question only, not the next one and certainly not the last one.
Keep your eyes scanning around the screen, I think ATCO's call this 'the flick' and try to prioritise as best you can. I decided I couldn't do most of the maths questions AND keep all the planes flying so I prioritised the planes and only did the maths questions if I got chance.
I'm not saying this is the right way to do it, but a) I passed and b) I guessed keeping the planes flying might be a key skill for an ATCO
Good Luck, you'll do fine