This is different for everyone. It is a lot of work. It took me eight years and two novels to get my power system down. There are just so many parts to it. Start small. You just need an idea. Doesn't need to be fully fleshed out. You can do that later. Research a lot throughout the process. Research helps.
Don't Limit Yourself
If you've been following this blog, you've probably noticed I don't refer to my character's powers as magic. It's not magic. Don't think because you're creating fantasy, that the powers have to be magic and spells. They don't. It's fantasy. The power system can be whatever you want it to be.
This goes along with don't limit yourself, but I had to make this separate. You can create a race of creatures that shoot light beams out of their ears. If you put the proper work behind it, this will sound believable. Don't be afraid to be out of the box.
In one sentence or phrase, describe the system you want. For mine, the characters draw energy from Darkness. Simple. What's you're idea? Remember, it doesn't have to sound believable, yet.
Race of Beings
Who will use this power? This does not have to drawn out. You just need a name and what makes them different. For the short story that started The Sciell, the creatures were called Shadows because they could collapse their bodies into shadows. I did a Google search to find out if similar creatures existed in mythology and I came across Carl Jung's idea of the Shadow.
The shadow, said celebrated Swiss psychiatrist C.G. Jung is the unknown ‘‘dark side’’ of our personality–-dark both because it tends to consist predominantly of the primitive, negative, socially or religiously depreciated human emotions and impulses like sexual lust, power striving, selfishness, greed, envy, anger or rage, and due to its unenlightened nature, completely obscured from consciousness. Whatever we deem evil, inferior or unacceptable and deny in ourselves becomes part of the shadow, the counterpoint to what Jung called the persona or conscious ego personality. (Essential Secrets of Psychotherapy: What is the "Shadow"?)This intrigued me. I read somewhere else that Jung believed the shadow possessed an abundance of untapped energy. And then came the light bulb.The shadow became the basis for my power system.
Knowing who will use the power can help created the power system.
Stories are inspired by something, so are power systems. You can pull inspiration from other books, TV shows, movies. Keep an eye open and a notebook or note app handy. You don't have to draw inspiration from other power systems. Notice, I created mine from a Jungian theory.
Next up: Fantasy Powers: More on the race of beings.