Here's a mouthful of a post that I did to get some advice, but I'll try to add more to the mix to better answer you.
When I was making my magic system, I was just 13. At the time I was bored, and I liked Skyrim a lot, along with Pokémon and many other things. I saw all the different elemental types that many magic systems in video games and fiction could do, and I thought : "What if I made one that blends everything, or at least as much as possible, while still making sense ?"
The rest is history I guess, I just thought about the basics, then added the fact you could blend stuff together. Once I got my elements, I also tried to think about each possible manifestations a spell could have. From an explosive projectile, to an erupting pillar to a shield to a curse to a passive property.
In the end, I had 20+ elements and around 30 manifestations.
Now put all the manifestations in a column and elements in a row ; and you got yourself a neat little array of every single spell that could ever exist in that system. And that's how the spreadsheet came to be.
The world building of it came after, and yet it helped with seeing the scope of it all so much better too. But you can see what happened here : it was gameplay first, lore second. It was the dynamic of the system first.
Now all that aside, since the start I knew what I wanted : Take as much "superpower" I could think of and make it make sense in a magic system. Bonus points if it can work in an RPG context.
So I think that if you want to make a magic system of your own, you got to ask yourself the correct questions first :
- What's the point ? What do I want to do out of this system ?
Do you want to complement something that exist ? Do you just want to have fun making it ? Do you want to make the magic system first then the rest ? Do you want to mix ideas from this media and that media ?
- In what context will it be used ?
A videogame ? A novel ? Tabletop RPG ? Can the system be played ? Does it need to be used ? If so, it needs rules, it needs to be understood enough so that it can be manipulated, it needs resources to limit it, whether it's mana points, spell slots or any other components.
Do you want your system to be special first and foremost ? Should it stand on its own, or should it help other things stand ? What makes my system so special to begin with anyway ? Find what you want do at the core, then make sure this aspect stands shining atop the rest. A solid core principle is much better than many smaller ones.
That should be all I can think of. If you (or any other reader) got any other question, you can always DM me. I'm always available to help people create (and be a nerd).
