I like the simplified style of the top one - but the shapes/proportions seem off. One foot is much larger, the pose is a bit awkward, and the face shape is a bit weird. It's also a little strange that the hair has no black outline, but you use the black outline for pretty much every other line in the character. The second one seems more consistent within itself.
All in all though, a solid first go at it. For pixel art tips - I'd recommend doing a TON of research on pixel art and sprites that really inspire you. Download sprite sheets and animation gifs, study them, try copying them a bit for practice, and apply the techniques you learn from them to your own work. I keep an inspiration/research folder on my computer at all times, that I'm constantly updating and studying. From there, it's just lots of practice! There's also plenty of tutorials online to help you get a solid base.
Oh, and practicing regular drawing is also invaluable. Pixel art is its own medium, of course, but learning how to draw people, animals, objects, etc regularly without pixel art will really help you with your pixel work. Don't have to be amazing at it, but understand form, line, and value will help greatly contribute to the quality of your pixel renders.