if you have a list of colleges you're looking at, check out their audition requirements and start trying to gather ideas about what you might want to use for your pieces. i know it seems early, but if you start preparing now, we won't see a thread from you in a year that says "I HAVE AN AUDITION NEXT WEEK AND I DON'T HAVE A MONOLOGUE, WHAT DO I DO?!?!?" starting looking for material now gives you lots and lots of time and you won't have to be frantic about it.
keep up with your dance/acting/voice. also, keep your grades up. though some MT schools aren't too hard to get into grade-wise, having a good GPA and extracurriculars can't never hurt, even if you're applying to a conservatory.
also, check out college confidential's MT forum. it's the best resource out there.
College Confidential -- GREAT RESOURCE
"grace, you're stuffed in a box getting rid of ass plaque. let's face it, this evening is a bust."