I'm personally undergoing training now at Entry Point North in Sweden.
I would advice you to read Doc. 4444 (or the GB-equivalent), and familiarize yourself with the 50-100 most common aircraft (and their main specs such as max operational FL, cruise-speed)
We use 4444 quite a lot here in Sweden, or atleast we are supposed to be quite familiar with it ... For my part it would have been nice to be able to put an effort in a couple of months before starting the course.
Send me a PM if you'd like a copy of 4444 or our homemade "dummies guide to ATC".
Cheers
TH