I would actually suggest that, instead of paid freelance work (you don't yet have enough experience and your portfolio is very limited) that you try helping out project (like mine, shameless plug I know but hey, it's worth a try!) and joining pixel-art sites like PixelJoint and Way of the Pixel. Both sites have forums where you can post your WIP's and ask for advice... most of the community members are very helpful and will even give you visual examples of how you can improve your technique. They're also much better at critiquing work than I could ever be.

You could also try a website like OpenGameArt.org -- lots of freely available resources and and they could always use more AND there is also a forum there with several members that are very good at what they do who are willing to provide advice to pixel art beginners. Plus, once you've completed a WIP and are satisfied with it you could release it for programmers (like myself) to make use of.