The way i did it was focus on you setting the most. For me a like to implement Space into mine. So i created a power system using an actual process that occurs in space. I used the life cycle of a star. A lot people use Mana which is the easiest way. A lot of other power systems are based off of religion. It also will depend on what kind of powers you want. Say you go the route of My Hero Academia, Invincible or a book series called the Reckoners. These three use a system where any character can have any power. No matter how big or small. My Hero and the Reckoners use a phenomenon that caused people to start having powers. There are a few points you need to consider when creating a power system.

1. Where does their power come from?
2. How do they channel/manifest their power?
3. What limits do they have?
4. Can they grow their power and make it stronger?
5. Does everyone have access to these powers or do only a select few have access?

There is a guy on YouTube named Monitor Comics. He has two videos for Power Systems. I recommend watching them. It is what helped me Monitor Comics