Great question. There are many factors to consider before taking summer classes before your first college semester. Have you already have declared a college major, and if so, is it hard to take classes to fulfill the major requirements based on the sheer volume of students wanting to take those classes, leading to long waitlists? Additionally, are there any classes that you would like to get out the way, such as a math class, before you start college? If you answered a definite yes to these questions, then you may want to consider summer school. Summer classes are condensed courses, with a lot of material packed in and are usually much quicker paced than a course throughout the semester.
Since this is the last summer before you start college, you may want to also consider just enjoying the break, spending time with friends and family, going on trips, or any other hobbies you may have. You will have the opportunity to take summer courses during your college tenure as well, but I also recommend looking for internships during the summertime, once you have completed your first year of college.
Hope this helps,