It's a good start. The eye is especially good, and I like that you've chosen blue as the background, because it is a good complementary color to the red of the horse.
With acrylic, you need to probably use more paint and paint more layer and thicker color. I find acrylic very challenging, and hardly ever use it. I prefer the way watercolor does a lot of the work for me with it's unpredictable, but gorgeous natural movement (wicking and running and blending) with the water ,color and the paper.
Use more paint, use complementary colorse to create shadows and get some lights in there . Overall feeling is too dark.
complementary means across from each other on the color wheel.
such as yellow - purple
orange - blue
red - green