Long ago and far away, I ran an AD&D campaign. It was the first time I had tried a free-form campaign, using minimum preparation, but making notes during.

The Beginning

AD&D, first edition... sort of.
No psionics, no monks, no thieves.
All the players started out as humans.

You make up a tenth level character. Give him whatever stats you want, but be moderate. One 18 is okay, I will edit you vindictively if the scores are too high.
Max out your hit points for your level and con.

Make up an equipment list. Anything non-magical that costs mere money, you can have.
Make a list of magical items you think you should already have. Be moderate. Again, I edit vindictively.
Now, make a "wish list" of items you would like to have. Don't rely on the things in the books -- make up things and give me details of how they work. Limit of ten items, but if I disallow something, you can replace it with no penalty.
The "wish list" is returned to the player with two "ingredients" after each item. If the character can find these "ingredients," he can return to Cambria and have the coveted item made for him.
The "ingredients" are not always included in the making of the artifact. Sometimes, they are just part of the price asked by the manufacturer.

One of the players was a cartoonist. He drew an ogre in a strait jacket, shivering. The caption read, "They didn't run! And they pulled out these shopping lists. One of them shouted, 'The liver's mine!' "

The World and its Magic

The world was divided into three regions. Most humans lived in Cambria, a fairly mundane area where there were mages with spells and clerics with healing powers, functioning according to the descriptions in the rule books. Beyond the borders of Cambria, under a perpetual soft twilight, was the land of Faerie. Magic worked differently there, just how differently, the characters had to find out. Between the two was the Midworld, where magic worked differently in relation to how close a part was to Faerie or Cambria.

The best explanation of magic in Faerie is the analogy of low light photography. Imagine a world of dim light, with a finely developed art of photography. All of the techniques are based on known levels of light, never exceeding a certain level, and capable of resolution under very little light.
Now, export this photography to a world of normal light. Your equipment works -- works all too well! And there are colors and reflections you never imagined.
Magic learned in Cambria is very powerful in Faerie -- almost too powerful to use.