Hi Jennie welcome to pixelation! The tutorials thread is a great place to start, as philipptr says. I think you may need to start a little before pixel art though, if that makes any sense. This is a tutorial by a non-pixel artist that has had a huge influence on how I do pixel work:
http://www.itchstudios.com/psg/art_tut.htmThat is linked from the tutorial's thread as well, but I am terribly fond of it, because it's kind of like a cheat sheet for art. Good, simple explanations and nice little diagrams to explain some of the basic rules of 2D art period, irregardless of the medium (paint, digital, pixel, whatever).
Another good thing to keep in mind as you start your pixel experiments is how you are going to treat your outlines on each piece. Developing a consistent approach will help unify your pieces in a big way. That art fundamentals tutorial is much more important than this, but this is something that you could easily do to both your plant and your carrot to improve them some. For example, if both the plant and the pot featured a black outline, they would look like they came from the same world. Likewise, if the both the carrot and the carrot's planty top had dark outlines, they would look more unified.
Finally, a great and easy way to start down the path of good color choice is to work on a neutral, grayish background, rather than white or black. It will be weird at first (because paper is white, right?) but it will be a huge help to you!
Again, welcome to pixelation, and I look forward to watching both of your progress
