The best thing to do is get a fast lens (f/1.8 or faster). I would assume there is going to be a lot of motion, so to avoid blurry images, you'll need to shoot at a high shutter speed (1/500 is a good place to start). However, high shutter speeds require a lot more light.
Depending on the amount of light, you'd likely need to shoot at a high ISO too. With that camera, I would try to avoid shooting at anything over ISO 800 to avoid a lot of noise.
Best mode is Manual. Try setting the ISO to 800, use the widest aperture you can, and then do some test shots beginning at 1/500 and see what will give you a good exposure.
Also, since the flash will only sync up to 1/250, that still may cause some blur, but will help freeze the action. You just may need to put a color gel over it to balance the color with the available light. My guess would be that you need a CTO gel, which will make the light from the flash more orange to better match the lower color temperature of indoor lighting. Just depends on the lighting.
Hope that helps.