I think this looks pretty god for a pixel virgin. No hard outlines!
The composition looks good. Your palette could do with a a tidy up (look at how you space your colours in terms of value and saturation) and some of the forms are a little indistinct
You've got a definite light source, which is a big plus, but I think you need to be a little more confident and in places use highlights and shadows close to each other. This will help to really define the form.
I think this will help
http://derekyu.com/extras/pixel06.html