1. Use your intelligence and self-teaching skills to make sure you get the best grades possible; this will help you get financial aid for college. Otherwise, you'll be limited to cheap schools, saddled with debt, or unable to go at all.
2. When you have choices about which classes to take, take ones that stretch your creativity in areas you wouldn't normally explore: for a geek, that's probably art, music, literature, philosophy, wood shop, metal shop, etc. These classes will usually have you creating things which is fun, and if you're creating written papers, that's very good practice for your future.
3. Since you're smart, #1 shouldn't take up much of your time. While in classes you can't avoid, you can 'take notes' writing about something else you're working on. Pay just enough attention to the class to make sure you're following what's going on. Outside of class, SOCIALIZE. Learn to make girls smile at you (or boys, if that's your thing.) Learn how to make small talk, and how to get someone else to talk about themselves. Having good conversational skills, especially if you're introverted, will be hugely important for you in your future.