The way to make anything pop out is CONTRAST. That's the key word.
I'm going to go ahead and say that learning color theory and colors digitally is so much harder than traditionally, where you have to actually think about the colors you're mixing. I had to pick up guache for studies, and honestly it helped me a lot. And learn from references and still life. STILL LIFE IS DA BEST.
Anyways, think of it this way, and I'm not relating this to your character or the lack of a background, it's just an analogy.
To make a character pop out from the background in a 2d top down game there's a few options, but the main one is to use colors. Make the background generally use desaturated colors and the characters use saturated, brighter colors. The DIFFERENCE is what makes the CONTRAST, and lets you as the artist control where the eye goes.
I hope you get what I'm getting at. =p
Disregarding colors, the character seems noisy, and the form is hard to read, the character seems flat. You're overcomplicating the character and I feel like you're trying to add too much detail. If you want to learn something art-wise, remember that pixel-art is a stylization of the basics - it's important to have fundamentals down before if you want to reach a very high level. That includes but isn't limited to perspective, proportions, light and shadows, simplifying shapes, anatomy and so on.
I am biased and it shows, so take what I say with a grain of salt, but I feel that learning outside pixel-art is the best way to improve.