The top of my son's chest-of-drawers is his altar. It has this neat little wooden "bench" that I found at Marshalls on it, and upon that he has placed various statues of importance to him -- and then around that other things that mean something to him. We try to keep it clear of other things, but sometimes (since he is 8) there might be a book up there too, or a hat... Regardless, he is known to light his own prayer candles (with my permission and supervision ONLY), incense, say prayers, chants, etc. in his bedroom with his altar.
I would place upon it things that mean healing to you -- that symbolize what you're trying to concentrate on. Really, an altar can be anything you want it to be, and have upon it anything you wish, or nothing at all!!
Here's a pic of his altar:
Be creative.
Enjoy!
Grassaf,
Becca