What can I do to improve my photography?

I'm a freshman in High School who started getting interested into photography a year ago. Anyways, I consider myself an amateur and consider getting a good camera to improve my photography (maybe a Nikon D90 or Canon 550D). On the other hand, there are photography class and yearbook in my school, should I join those classes? Please go to my flickr page and suggest anything I can improve on: Thanks!

At this stage, a class would be far better for you than getting a new camera. With a more expensive camera, you would have better resolution shots with greater dynamic range. However, you would not have changed the most important factor in good photography: the person holding the camera. A class would help. So would joining the yearbook. Associating with other photographers who learn from each other is a quick and fun way to improve your skills.

You might end up killing two birds with one stone because the class might require an SLR or equally capable camera.

Once you have figured out how to use your camera to produce perfect exposures, the next step is to.refine your composition.

http://photoinf.com/General/Robert_Berdan/Composition_and_the_Elements_of_Visual_Design.htm

Of the two cameras you listed, the Canon is an entry level camera and the Nikon is a more advanced camera.

NO camera will improve your technical or creative skills. Those skills are up to you to learn.