As my drawing instructor in college would say, 'The difference between a good artist and a bad one is a stack of crappy drawing this tall', *holds arms as far apart as they can be*. Just draw - constantly. Every day. In every medium that you can.
Drawing in pixel art is really no different from drawing in any other medium. Improving your art skills overall will make you a better pixel artist. Two things to get you started: 1) Use reference material. Look at photos, go outside and look around, and constantly study the world around you and how light interacts. 2) Learn to draw from real life and then adapt that to a style you want to execute. Trying to learn from other styles will simply degrade your skill set and hold you back. Instead of trying to learn how to draw by studying, say, manga. Learn how to draw from real-life and then apply manga style techniques to that.