Obvious question? Possibly, but the answer's intended to be reassuring.
First, rest. The point of holidays is rest. It's a point that's often lost. There's no point in doing the heavy lifting part of revision if it means you start the next term exhausted and ill. Build in some rest at some stage.
Second, relationships. During term, time can get squeezed. This means young people spend less time with parents, siblings, extended family and non-school friends. Much of what we understand by quality of life comes from these relationships. Holidays are when they should be fed (and that means, teenagers, you should do the washing up more often in holiday time!).
Thirdly, revision (at this time of year). It's no good leaving your revision until a month before the exam. By the time you go back to school, you should have done your learning, because your teachers will be running through the final elements of how to use your learning to perform well in the exams. Work intensively in the holidays, and work a lot. See the next post below for more tips on this score.
So, it turns out that not only is term time about the 3 r's, but so is the holiday: rest, relationships and revision. If you don't have public exams next term, substitute reading for revision, and the same applies.