How to sell cover songs without infringing copyright?

I have seen many good artist on YouTube that make covers of popular songs. Some even sell every song they record. As I am starting with recording cover songs myself, I would like to know what needs to be done to sell a song and not infringe copyright at the same time?
All I have noticed so far is that they slightly change the lyrics. And of course they record the instruments on their own.
Is there anything else I’m missing that needs to be done?