This is a great start. You have a pretty amazing natural ability at something which is really difficult in pixel art: which is showing a full object/figure/whatever in a very small space clearly.
However, obviously there's a lot to be learned. One thing pixel artists look very carefully at is their line work. Many use line cautiously and sparingly; other's choose to remove it entirely (as outlines are simply unrealistic, they generally don't exist in real life). But very often they are necessary to separate different segments of a figure (such as the hair and head in your piece's case). I would recommend to you attempting to remove the outlines from your piece entirely and seeing if you can make it work without them. You may find out this is not necessarily better for the piece, but playing around with different approaches will help you learn pixel art all the more faster.
Also, your piece lacks any sort of shading. Sometimes, because of the limited space of a work, a single tone can be enough for a part of a figure. But if a pixel artist can successfully add a highlight or shadow to their work it can make that part pop all the more. I would play around with shading the hair of your character. Try adding a highlight or shadow to the one tone you have now. Think about the direction the line is coming from onto your character (perhaps from above him) and then apply the highlight or shadow where you would think it would hit the hair. To really make the shading pop, use a color that is highly contrasting with the one you have already. Often times the more contrast you can get away with between shades without losing the illusion of a single surface the better looking a pixel art piece will look.
Anyway, these are just some general ideas to get you thinking about what you can do with pixel art and how to approach it. This is a really great first piece and shows a lot of promise.
