A few design tips/thoughts for what they're worth then:
1. Prototype games, get people to test them and then improve on your work based off their feedback. Working through that sort of process is really valuable for your own development and gives you something you can talk about at interviews and use in a portfolio to distinguish yourself from other candidates. Bunch of different ways to do this (mods, flash games, board game/roleplaying paper prototyping etc).
2. Play a variety of games and play them critically. If you're not already in the habit of doing so I'd recommend putting a bunch of thought into why things are done the way they are, how they could be better and why those better alternatives may not have been chosen. In particular make an effort to play stuff from genres that aren't normally your thing and good older games you missed for whatever reason. It's possible to learn a bunch from games you wouldn't play just for fun.
3. Get practice working with people on joint projects, beyond just what will be involved in your coursework. Game development's a really popular industry so being able to demonstrate you can work well with people's really valuable. I'd expect you'll get some of this through your coursework of course, that's amount's going to be the average for applicants from a similar background though and you ideally want to position yourself as well above that average.
4. Focus on learning transferable skills, not really specific technical skills. Knowing a lot about a particular tool or scripting language isn't necessarily going to help so much if the companies you want to work for do their design in something else. Being able to pick up their tools and being able to convince them that you'll be able to do so quickly on the other hand's really valuable. This one's a bit nebulous and a bit of a 'learn how to learn' cliche I realize, but a lot of people do seem to get obsessed with mastering a particular tool rather than developing a wider design skillset.
Hope this helps a bit, good luck with your study!
Thanks for the tips, since I'm thinking about going in the industry, I guess it'll help me!
However, I had a questionning about my... let's say. Artistic knowledge.
Does a game designer need to be able to draw?
I mean, doing the visuals don't really seem related to game design (I mean, gameplay design. That's where I want to head.), but doing prototypes, flash games, etc... and such requires a certain artistic technic, doesn't it?
And since the only artistic medium where I consider myself having the ability to efficently convey my message is literature... Humf.
...That must sound weird coming from someone whose grammar and syntax is clumsy, but English is my second language, be gentle, I'm working on it! :P
Even if you can't draw though it's well worth trying to develop your understanding of visual cues, artistic approaches, elements of visual art etc. Appearance is a key part of design, in terms of satisfaction, partnership with artists and conveying information to the player in particular, so learning what you can's going to pay dividends for you.