I just took a look at your gallery... I see your avys are the right size, and show that you are trying to make them, which is great
...I think you should work some more on making blendable effects, and bringing out colors... since you already show that you wanna put some effort into graphics, which is great, this shouldn't be too hard...
I recommend you read though this faq [link], look at the sites under [How do I get started] and then try to learn how to make bendable effects with a picture...
Once you have made say 3 - 5 avatars after learning from tuts... you should come back and reopen a shop... who knows, you may be able to charge more too...
If you have any questions after looking around, be sure to ask...
Cheers and good luck