A post that has been reposted in a number of old thread, so I am putting it here for people to see and reference
Magik is fun….
Everyone wants to make a magic system for their game, be it THEIR GAME SYSTEM or another. So have fun and do it. Just a few things I want you to think of.
1) Treat your magik system like a character.
Start with a conception… what do you want magik to be like… what do you want it to do? How powerful do you want it? Once you created a conception for it, it makes it easier to do choices.
If you want magik to just grant modifiers to die rolls, you just have two spells. If you want lots of combat magik, figure out what kind of damage effects you have and scale them about the various levels of effect. A great way to create this conception is to choose a book (or existing game system) and say, "I want my magik system to feel like… insert book/game." This gives you a guideline for what is acceptable and what is not.
2) From there, choose what kind of game mechanics you want to use. You should use the same mechanics you are using for your skills to resolve magikal actions, but some people insist on multiple resolution systems in the same game.
3) Tinker with your mechanics until you get something that might work
4) You can always get a group of your players together and have them do the grunt work for you… So if you want a huge spell list, have your players start making spells up.
5) A big cheat to avoid writing up spell lists is to make types of spells a skill. So you can make a list of guidelines rather than a spell list,
6) Check out what others do. There are dozens of free fantasy games that you can look at on the net, currently. There are five or so free open source netbooks of d20 spells out there.
7) You can post it up here, but remember we need information to make comments. So instead of saying, "I have a cool magic system," we need you to explain the system and the world, so we have an idea of the magic we can help you with.
8) Remember, you have to write it up so people can look at it. Remember to put it in a format that people can understand, that ideas flow (being explained) in the text, and remember that you will need to write up all those little details eventually, you might as well get started.
0) Might I suggest hitting the game design forums. The two best are www.rpg.net , and if you are serious about this, www.indie-rpgs.com known as the Forge. RPG net has a design forum that is frequented by some small game companies, as well as a general community. The Forge is for serious game designers, so I won’t recomend it for you, but I if you want to go….