If I believe in a coin/project, I hold as long as I need to. If I no longer believe in a project, I'll sell. However, I'll never sell at a loss unless it's to reinvest into a better project.

How do I determine if a project is good? See if the team is actually working. Is there a wallet, are they updating the wallet, what are they working on, are they meeting deadlines, etc. So many crypto projects release nothing and people buy their coin anyway.