If you have art that is PIXEL ART ONLY, you should post it in the Pixel Art part of the forum. Once you have turned this sketch into a nice pixel art sprite, we'd be happy to critique it.
If you have art that is NON PIXEL ART, you should post it in the
Off-Topic Creativity thread. (But don't expect much critique. There are plenty of good traditional art forums out there if you want critique on your sketches.)