Kim McAuliffe (1995, Game Designer, Microsoft Game Studios): Play games -- and not just the games in your favorite genre. Play what your mom is playing on Facebook and figure out why it's so compelling to her even if it's not to you. Play things normally out of your comfort zone. Being able to talk about any genre at will is valuable. Play board games, card games, everything. Analyze the major systems as you play, figure out how they work together to form a cohesive experience, decide what you feel works really well and what you think is broken. Know what rubber-banding is. Notice when something feels too random, or not random enough. Modify the rules; create your own.
In every interview I can remember, I've been asked, "If you could make any game, what would you make?" Have an interesting answer ready for that, not just "I really want to work on Sequel X." What would you do that hasn't already been done? Also, do your homework before interviews. Play the company's games and dissect them. Talk about what you like, but more importantly, talk about what you don't like and how you would change things to make the game better.
Be willing to start out as a level designer, and play with level editors to create your own. It might not be possible to leap straight into systems design without prior experience, and on smaller projects/teams, you might be called on to do both. Even if you don't end up in level design, you need to know what level designers do.
Be multifaceted. If you're in school, take classes in writing, art, programming, and public speaking. Being able to organize, explain, and present your creative ideas is as important as generating them. You will be writing documents for an entire development team and/or clients to read, so they have to be clear and concise and use good grammar. Having a basic knowledge of what the artists and programmers who will be implementing your ideas do makes you a valuable commodity to hiring managers.
Stay current with industry news and trends. Add RSS feeds from major game sites to your daily reader; follow industry vets on Twitter to see what they think is hot and noteworthy.
The best tactic is to make a game. Having something playable that demonstrates your creativity, knowledge, and skill says more than an artfully written résumé.
I Want to Send My Idea to a Game Company. How Do I Do This?
Ian: You don't.
But you want to. How can you possibly get your amazing idea made if you don't submit it to a company? And why would they turn down your idea when it will obviously make them so much money?
For one thing, there's the legal system. If they so much as look at your idea and then they happen to come out with a game that has even a superficial resemblance, you might sue them. Game companies know this, so many of them will flat out refuse to look at anything you've done. If they do look at your work, it will probably only be after they have you sign a release form that signs away all of your rights to the idea, which probably defeats the purpose of sending it in.
Also, "ideas" are worthless in the industry. Just like everyone in Hollywood has a "brilliant" movie script they're working on (including the janitors), everyone in the game industry has at least one "brilliant" idea for a game. Ideas are the easy part; actually building the game is the long, hard, and expensive part. Give the same "brilliant idea" to ten different teams, and you'll get ten very different products. Ideas are nothing; execution is everything. A wonderful idea, horribly implemented, loses money.
If you want your game made, go forth and make it. If you don't have the expertise, you can learn the skills you are missing, or try to team up with someone else who can provide those skills (but you will have to convince them that it is worth their time to work on your idea, rather than their own idea, and the burden of proof is on you since you're asking for their time). If you have a working game, and the game is fun, that will get people's attention much more than an idea.