First let me say welcome to PR and the Sports forum. There are a number of very accomplished sports photographers here that can help you improve your photography and they are very willing to help. Secondly yours is a question that is ask a lot here and the short answer is there is no magic bullet. Conditions vary so drastically from one gym to another so there is no one setting that work every time. I would suggest however that you get out of any auto modes that you have been using and go to manual settings. You have all the camera and lens you should need to take good photos. Set the lens on your widest aperture and your speed at 200 at least to stop action (faster if you can get away with it). Adjust your ISO to a setting that gets you acceptable exposure and fire away. If you are still to dark or your images are still blurred the only other solution is to add external light. Hope this helps a little. I would encourage you to post a few examples of your photos, that will give us a better idea of where you are and what might help. Check out some of the other resent thread that address this same issue and you may find some additional answer.