You've chosen some good subjects for your pictures.
All you really need to do is watch your backgrounds more closely. As Pschlute suggested, take a quick shot to make sure you capture the moment, then move around to try and get a cleaner background. In the first shot, taking a step or two to your left, lowering your camera position, and zooming in a touch may have allowed you to frame the dancer against the trees and grass roof that's showing in the upper right of that picture. The darker background would have helped the dancer stand out more. In the second and fourth pictures, there are white objects in the backgrounds that are taking the focus off your main subject. On picture #4, try placing your finger over the white object that's growing out of the subject's neck and notice how much better the subject stands out. Btw, you've done a good job of blowing the backgrounds out of focus. You just need to watch for hot spots that will distract from your subject.