Studying programming will never prepare you for the horrors of having to deal with someone else’s code. But taking the time to understand what someone else has written is an underrated skill. The temptation will always be to start again – don’t be arrogant and assume that whatever you write will be better than what’s already there. You probably won’t have full context on why the developer has written that weird, unnecessary looking line. Think twice before you delete.
This works the other way round, too – in the future someone else is going to have to read your code. Be kind, comment your code.