What to genuinely learn before college ?

I'm prolly gonna be joining a low tier 1.5 or a good tier 2 clg for cse core by August. So in the meanwhile what can I do to improve my coding and computer skills. I'm currently learning c++ and was doing hackerranks for sometime, other than that what else would I need ? Yes I'm more than certainly enjoying my holidays but maybe it's that jee trauma that makes me feel like I'm sitting around and wasting time 😭😭 so I would really grateful if my dear seniors can help me out and especially tell me what are some common mistakes i should avoid as a first year