It's all about finding something you are extremely good at and love to do, and then finding a way to monetize it.
A lot of people make this mistake of not aiming long-term gain and going for quick-wins, forgetting that it takes a while to work just like any other offline business.
I wrote a comprehensive guide on the same topic: https://www.proficientblogging.com/9-best-ways-to-earn-money-online/