Finally, aspects have a passive use that you can draw on in almost every instance of play. Players, you can use them as a guide to roleplaying your character. This may seem self-evident, but it should be called out anyway — the aspects on your character sheet are true of your character at all times, not just when they’re invoked or compelled.
Not everything needs to be an aspect. Some things are about narrative permission — you can’t shoot someone unless you have a gun. No aspect needed. Some things are just cool, like having (an example from a recent G+ post) a double-bladed weapon. And if something is really key to a character concept, then that’s a character aspect, stunt, or just something you note down when you make your character — not inherently an aspect in and of itself.
That's maybe a bit boring, compared to all the crunchy magic systems floating around in the nether world of the net, but I really like to just stick with the plain core rules and do magic with nothing more than narrative permission. You want to shoot bolts of fire? Have a high concept that says you're some kind of battle mage, then roll Shoot and just do it. Mechanically, that's not any different than having your high concept say I'm A Gun Guy and rolling Shoot to fire your rifle. You want to empathize with the spirit of the location to find out what happened here? Have an aspect that says you're some kind of psychic, then roll Investigate. You want to summon a demon that tells you what's going on in the underworld or assists you in some ways? Have an aspect that says you can summon demons, then roll Contacts. You want to shapeshift? Have an aspect that says you can shapeshift, then proclaim that you do, and do what you wanted to do. So you're a wolf? Roll Notice (or Survival, if you have such a skill) to follow some tracks. You're a hawk and want to fly? Well, roll Athletics and do so. You're a giant gorilla and want to hurl trees at your foes? Roll Shoot. You're an elephant and want to trample down an enemy horde? Roll Fight and rock the ground. You want to create a magical artifact? Have an aspect that says you're some kind of enchanter, tell the GM what you want to create, have the necessary components at hand, then roll Crafts. You want to create a golem companion? Have an aspect that says that you can do so (being The Maharal of Prague usually counts), then take appropriate skills or stunts. Your golem should be really strong? Take a high Physique, or a Physique-increasing stunt. Maybe you are not strong by yourself, but if you want a permanent companion that is, you're spending your own character resources. (That's also true for all kinds of steady «mundane» sidekicks.) And so on. Of course, you always have to fulfill the fictional requirements of doing magic – or to use jargon, you have to have narrative permission. If it's genre convention that magic needs elaborate rituals and props, you have to have these props at hand and enough time to perform the spell. If you cannot do combat magic without having your blasting rod at hand, you cannot hurl fireballs without having that thing. If magic needs mana, and you took a consequence like My Mana Runs Dry (for example due to a success with a cost), you cannot cast spells until you have removed the consequence. Why I like that approach? Well, because it's plain and simple, and I'm a lazy GM. And of course because it just works.