If you haven't done so already, start building a relationship with the admissions reps from your top colleges. Send them an email or give them a call and state how interested you are in their school. Ask what you can do to maximize your chances of being admitted and whether there are tours or campus events that you can attend. Seriously: I've been told by many college admissions reps that they are more willing to go to bat for students who have communicated with them consistently, attended multiple events, and showed serious interest in their schools. This is especially true if your grades or test scores are on the border. In short, the commitment you show can make a real difference to some reps.
2. Request 3 letters of recommendation from diverse sources now.
Most students wait until the fall to request letters from their recommenders, which is when EVERYONE else is asking for letters. When your teachers and counselors are getting requests from 20 students at one time, they have less time to dedicate to each letter, and it takes them much longer to get around to writing yours. Trust me: I've been there. Cut the lines and ask for your letters NOW while your teachers are still happy and available. Some scholarships require 3 letters of recommendation, so I recommend you get 3 letters from different sources: a teacher, employer, community member that you volunteered with, etc.
3. Look up the early decision deadlines for your colleges and apply early.
I've been told by college admissions reps many times before: applying to colleges early often gives you an upper edge. For one thing, you're competing against fewer people, so admissions reps have more time to dedicate to reviewing you individually. For another, if you need to retake the ACT or SAT or raise your grades, you admissions rep can tell you early in the fall so there's still time to correct course and be admitted. Finally, those who apply early typically qualify for more financial aid! For most colleges, "early" means applying before November 1, but schools vary, so look at the early decision deadlines now for your colleges of choice, write them down, and apply early!
4. Start preparing a personal statement and your essays now so you can get them proofread by peers and teachers.
Your personal statement can make a real difference if you are on the border or if you are applying to small liberal arts college. Start writing your essays now so you can get them proofread by people you trust and revise them. For scholarship applications, it helps to have one really solid personal statement that you tweak for each application.
5. Participate in a meaningful service, internship, or leadership experience that will challenge you (and make for good college essay material).
Many college or scholarship essays require you to reflect on challenges, meaningful experiences, or leadership or service projects that have impacted you. If you haven't participate in something like that yet, now is the time! Take advantage of the summer to get involved in a project that will push you, help you learn, and make for great college and scholarship essay material in the fall. It's far better to have one sustained and meaningful experience than participate in 10 different events or activities that require little commitment or are short-lived.