Think of the potential clients you wish to cater too.
Don't pose or dress in a way that makes you uncomfortable, it will show in the photos.
If you are trying to portray a specific character, convey that, but realize that is how you'll be recognized, i.e. Children's Magician, Comedy Magician, etc. Don't fall for the cliché's of fanning/springing playing cards (unless you're exclusively a card magician). The same goes for posing with any magical props; you don't want to pigeonhole yourself.
There are SO many bad examples out there, it's easy enough to find them with a Google Image search.
As a personal example, I perform as a mentalist, so my photos portray as much.“Ars Celare Verum”
Magician - Illusionist - Mentalisthttp://www.mysteryandillusion.comhttp://www.facebook.com/MysteryandIllusion