There really isn't a lot of specific prep you can do for stage 2. The day is full of various different types of computer test, each one unique, and unless you have practiced the specific tests before (which you can't) I don't think there is a lot you can do in preparation to boost your performance. It really is a matter of either you can do it or you can't!
Although you can't practice the specific tests you will encounter at stage 2 one thing that might be helpful would be just to play lots of general different computer games. If you practice lots of games on websites such as
www.addictinggames.com this might help increase how quickly and efficiently you are able to pick up new computer based tasks and challenges - thus helping you to pick up the tasks you have to perform in the tests more efficiently as well.
Here are a couple of games I played before stage 2. None of them are anything like the actual tests, but they might help you develop similar strengths:
Multitask | Armor Games
I Love Traffic | Armor Games
ATC-SIM: a web-based air traffic control simulator
DACHSER Global Player Reloaded