Firstly, welcome to the forums and pixel art in general! I'm pretty new to it myself!
I really like your lineart. It is very clean and neat. I would, for coloring, start doing hueshifting! Its a technique to make your pixels more realistic, because nothing in the world shines pure white or casts a shadow of pure black or gray, its all different colors. For instance, with your heart, I would make the darker bits more of a purple tint, and maybe make the lights more hot pinkish, instead of getting lighter red. I would also add more colors to your sword, maybe add light blue for your shading. Color and contrast is a big part of pixeling.
Let me hop over to the computer and do a little edit on the heart so you can have a visual.
