(Now is a good time to clean up your online trail so that colleges won’t find anything bad about you when they google/facebook you. See these tips, these, and these, too.)
Browse schools’ websites, talk to recent alumni, visit the schools themselves and take tours, etc.) These posts list other factors to consider.
Start thinking about safety schools, target schools, and reach schools.
Safety schools = you have a high likelihood of gaining admission. In other words, your test score(s) and GPA are significantly higher than the median scores/GPA of these schools. Such schools may be willing to provide you with significant financial aid in an attempt to woo you into accepting an offer of admission.
Target schools = you have a decent chance of gaining admission (perhaps 50-50). Your score(s) and GPA are about on par with these schools’ median scores/GPA. These schools may provide you with *some* financial aid, but they’re unlikely to give you a full ride (a full ride would be admission without having to pay any tuition at all).
Reach schools = you have a relatively lower likelihood of gaining admission. Your score(s) and GPA are significantly lower than these schools’ median scores/GPA. These schools are unlikely to provide you with significant financial aid, but going to such schools will likely provide better employment prospects and prestige upon graduation.
A sidenote: rather than applying directly to colleges, you may apply electronically through the Common Application website. If a given college uses the Common App, this website is the centralized information processor for your biographical information and college essays.