The Canon T2i also known as the 550d is a great camera for digital photography enthusiast's and those just starting a photography business. With a little practice and allot of patience you can get amazing photos and video from this camera.
Tip #1 for the T2i is to read the owners manual and become familiar with all the controls. Now you may be saying well duh! However too many people just grab the camera switch to one of the automatic modes and start shooting. The automatic modes are good but you will begin to realize that you are very limited in what you can accomplish.
Finally don't be afraid to experiment with different settings. Just remember what you did and try to understand why those settings gave you the results that they did. Also your camera came with a log book so I suggest, at least in the beginning that you use it. Writing down what settings worked may help you understand why later.