Sophomore Summer
The PSAT is one of the more important tests you will be taking and you need to begin studying for it early. Study now; don’t wait until after doing poorly to regret not studying.
Link: PSAT
The single most important test of high schools is probably the SAT or ACT. These tests are generally considered to be the primary college admission exams. Again, don’t wait until later to start studying. Do it now. Studying for the SAT will also help with your PSAT studying, so you’ll be killing two birds with one stone. Decide whether you want to take the SAT or ACT and then start studying.
Link: SAT
It is also a good idea to take classes over the summer at your local state university or community college. These classes often count for credit at your high school and/or can be counted for credit when you go to college. They are also a good resume builder because they show your academic competence at college level courses. Lastly, because you can choose from a wide array of classes, you can pursue your interests and become more knowledgeable and skilled.
Link: College classes
Participate in a camp or summer program. These are usually great experiences that also serve to give you a better idea of your interests while building your resume.
Link: Summer programs
You’ll probably have some time the summer before sophomore year, so search and compete for scholarships. There are thousands of scholarships offered every year, most of which require a simple application and essay to compete in. Improve your writing abilities, win accomplishments for your resume, and earn money at the same time.
Link: Outside Scholarships
While sophomore year is busier than freshman year, you’ll still have more free-time than you will later on so sophomore year, especially the summer before it, brings another great time for self improvement and accomplishing goals that aren't necessarily academic. Physically, intellectually, musically, or any other way, you can improve yourself. By now you probably have a somewhat less nebulous understanding of your self and your interests--pursue these. Excel at them. Make the most of the freedom you have this year.
Link: Self-Improvement