Reading, writing and math.
Go to school, get good grades. Improve your writing skills.
Go to college for game design, or writing, learn some programming language(s), but only after you have learned english(assuming that is your native tongue).
Game Design is a job, like any other job. Approach it like you would any other job.
Within the design field there are several sub-catagories for you to apply. Level design, quest design, story design, technical design, etc... You need to know how to do them all, but you need to really excel in at least one.
I'm going to go ahead and disagree with these toolbags and tell you NOT to play lots of games right now. Go do your homework and get good grades. AFTER you've finished your homework, then play games.
It's important to note as you play the games what is good and bad. What feels natural or intuitive versus what isn't.
Most of all you need to improve your writing skills before you pursue a career in game design. Written and oral communication are a must in any field, but ESPECIALLY for a job that entails a lot of writing.