If you look at fantasy drawings and paintings, wizards tend to have
the same characteristics: a long robe, a long white beard, a pointy hat, and a staff.
It certainly ia the description of the most famous wizard of them all: Gandalf, the
creation of J.R.R. Tolkien.
To generalize a bit further, a wizard tends to be quite fragile, not very muscular,
depending more on his magic than on his muscles.
A sorceress can be the female variant of a wizard, like a witch, but she can also
look like a powerful, beautiful woman that can bend every man and demon
alike to her will.
Wizards of the Coast, the company that bought TSR and thereby all Dungeons and Dragons stuff,
published a lot of pictures online from the old game, and some from the new third edition
game. Take a look at Wizards of the Coast to get those
pictures. Most are real good and give you even more ideas on creating your wizard or
sorceress than you already had.
For the preparation fase you'll need to decide how YOUR wizard or sorceress looks like.
I wanted to create a mix between a wizard and an alchimist. Which brings us to the next
part of the preparation: making sketches of the figure you're going to make. Even if
you say "My wizard looks lust like that picture by Clyde Caldwell" that's not enough to
create it in 3D. Try to visualize how the wizard looks from the side, from the back, etc.