What should I do during the summer?

In terms of recruiting, right now coaches are the freest to talk to you. They are handling paperwork for their incoming freshman athletes, planning the season, budgeting, etc. Office type of stuff. Which means now is a good time for you to get to know them. Schedule phone calls and skype calls, ask questions and understand what they expect of you. The more of a personal relationship you develop with the coach, the more likely he is to vouch for you whether it be admissions or scholarships. If you are a rising senior in high school, start on your college applications. Study for SATs if you are taking them again. Just because you're not in school doesn't mean you get to slack. The grind never ends.