- Not a fan of the "pelvis outwards, legs bent back" stance. While I did once use it often, as an amateur spriter, it's something I do regret now. It seemed pretty uncomfortable and unnatural for an idle position. Another common trait that sprites like these usually share, for some reason, is where you seem to begin to lose your grasp of anatomy on the limbs. They're basically tubes that get wider as they get closer to the fists and feet. I'm also confused as to how his head manages to remain attached to his body.
- Try not to build on a silhouette if you're just working on a basic body. Silhouettes would be better for exploring dynamic designs, for example, if the character has a lot of accessories or garments attached to him that would alter his/her silhouette (or if the character itself has a different frame). Even then it's probably better for more experienced artists familiar with anatomy, proportions, perspective, etc. If you just want a figure, building up from a frame to basic shapes is a good way to go.
- Banding and flat shading are two things almost featured in the sprite. The outlines seem to be serving as a crutch here. Namely on the limbs, highlights and shadows are placed around them, disregarding basic forms. On the final sprite, this is fixed in a few places, but then the direction of the lightsource is unclear.
- Palette is very saturated, yet rather bland. As far as I can tell, the only common colors are shared with the eyes and shirt. (Aspects of the sprite sharing common colors is a pretty good way to create a sense of unification, so long as the colors aren't too far from eachother.) Aside from that, there's no trace of, say, hue-shifting, which is tinting colors to a certain hue depending on how light or dark they are. For example, dark green would be tinted towards blue, giving it more of a dark teal appearance, while light green would be tinted towards yellow, thus, a yellow-green appearance.
With those points overwith, here's an
edit redo.

Left to right:
1. Your character base for comparison/reference.
2: With an idea of proportions I want to convey, the basic frame is drafted.
3: Moving things around, correcting mistakes, face, shading, and general bulk added. (Some mistakes.)
4: Adding clothes and accessories, redoing face to something closer to what you have. Toning down overall saturation to something less cartoonish to something possibly more realistic--not sure if that's the direction you wanted to go in, oh well.
5. Your final sprite, also for comparison/ref.
By the way I'd like to know the context of this sprite. If it's some kind of character selection portrait for a roster, once again, you'll need a better pose, one that says something about his personality/character; more than "I like to lean backwards and stare at things". Or you could use a portrait. If it's for actual gameplay, the feet need adjusting, and my first point still stands; its pose seems rather uncomfortable.
Hope this helps.
EDIT: Huge unrealistic hairdo, pretty stereotypical for the character type and doesn't help with the balance, I think. I also have a feeling the previous sprite's eyes were better... Which isn't saying much, both seem pretty feminine, being wide-eyed shiny and eyebrow-less as they are. I'm assuming this character is male for a few reasons, in which case they're pretty unfitting.