How should I take pictures of dancing?

My sister is on the varsity dance team and I have a really nice camera but i have been shooting more flowers and stuff not so much moving objects. I took some pics of her dance today and alot of them seemed like the camera was focusing more on the background and less on the grils dancing, as a result most of the pictures i took were blurry… I was just wonder what i should do, settings, iso, anything that could help i would be very thankful. I'm taking pictures with a Nikon D3100 on the sports setting with a 55-200mm VR lens… Please help they have another dance tomorrow and i would really like to get some nice shots.

What ISO are you using? Try raising the ISO to at least ISO 400., maybe higher. Experiment!

You need to be in a larger focus mode. Center focus will focus on whatever is in the middle of the pic. You also need Full-time servo AF, see pages 38 and 55 of your manual. I'd experiment with Dynamic-area AF and 3D-tracking since they are moving, see page 58 of your manual.

See if you can get your sister(s) and mother and friends to fake a dance routine so you can practice before the big shoot.