I'm a beginner coder, I know for the first 4-5 contests my rating will only increase even if my code doesn't get accepted. My question is, after the initial 5 contests, how to know how many questions to solve in a contest considering the user Rating, the number of Previous contests he has given, and ideally under which time he should submit the code to NOT DECREASE THE RATING?

I'm asking this because one of my friends even after solving 1 question of division 2, his rating decreased twice. So, I can avoid this in the future. It would be super helpful if someone give some more insight into this, thank you.