Well, all you need is to practice your brain, like playing tetris and such.
I can say it was difficult, but if you feel confident about yourself you can do it! I'm a huge aviation geek (I even have a virtual airline and I have over 700 hours of online flying) and it kind of made it a bit more easy (won't make a difference in Eurocontrol, but in NATS it will).
Well, I just got offered a place in NATS and I can tell you that it will be difficult, but it is rewarding!
Good luck!