Wow, I am in the exact same position. I decided this weekend, to no small damage of my pride, to push any and all programming aspirations aside and concentrate completely on art from now on into the foreseeable future.
Okay, some advice:
To start, you should join any pixel art related challenges you can enter. We've got a photo palette challenge running here, and Pixel Joint has a new challenge every week.
Second, I'd recommend you think of a game you'd like to make, and mock it up. Mock ups are good in that they get you creating stuff you normally might not pixel in little one-off practice pieces. By doing this you'll have to tackle rendering a complete scene: terrain, structures, people, animals, etc.
Finally, and most importantly, sit down with a sketch book or some computer paper and draw. I like to browse thru deviantArt and tumblr and just draw stuff that stimulates my id. Naked girls, robots, girls, space ships, girls, military vehicles, girls, etc. Copy other artist's drawings, draw from photos, draw something out your window, take a drawing in someone's style and draw it in your own style. Grab some colored pencils while you are at it and work on color composition.
Really, before you work in any medium, digital or otherwise, your first instinct should be to whip out a pencil and a piece of paper and think things out visually. Get those juices flowing.
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Other than that, just work at it. Pixel art is a skilled trade. The more you put into it, the more you get out of it.
