Just some general tips, not a fullblown modeling tutorial (sorry).

Get something down on paper first! Having something to use as a guide while modeling will help tons. To the left is a quick sketch I did of my character before I modeled her in 3D. It's a crap picture, but it helped me decide on a color scheme and some clothing ideas first.

If possible, draw front and side views of your character and bring them into AM as rotoscopes. Or you can go to websites like How to draw manga and find pictures to use as rotoscopes. (Also a great place to find ideas for clothing, hair, face and eye styles, etc).

Folds are good! try to work a lot of folded cloth into your models, they break it up and make it look very spiffo.

Here's a wireframe of the head.. it's a good idea to model the eyebrows seperately from the head mesh, because if they're part of it they wont get toon lines and they're hard to make out. The eyelash is modeled into the eyelid.
Hair is a pain in the ass!! Lathe yourself a strand (4 sections), then tweak it so it's not round but more diamond shaped.

Then just start plugging it into the character, rotating bits here and there til you get it just right.

Here's a front and side view of the model in wireframe. In general try to make your shapes as smooth as round as you can, at first my character had a pretty "ripped" look .. lots of muscle definition .. it didnt look so great, it improved when I took all that definition out.
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