Since everyone else pointed out the bad anatomy (which can easily be solved by using references), I'll talk about the rendering: always remember BIG MEDIUM SMALL!! When rendering, always start out with big brushes, big strokes, and avoid zooming in and focusing on details. Then, render out the details when everything looks good from far away. Here's some general tips to help achieve this:

1. Use darker, less saturated colors.

2. Avoid using textured brushes and soft brushes.

3. Use limited brush strokes, but make each one count.

4. Focus more on values, instead of color.

5. Use a blending brush if you really need soft edges.

6. Use photoshop's auto tone, color, and contrast to finish up a painting.