Hi Kriss, I think that's a great shot! Presumably you were using your 70-300mm?
For the best JPEG quality, always shoot in Fine mode. RAW mode can give you a little bit extra, but you need to convert them on your PC or Mac later and I don't know if you're up for that.
So for now, choose Fine from the Image Quality menu and L from the Image size menu to make sure you're also using the full resolution of your camera.
Those slightly fuzzy marks you can see on your image though are from dust - and I'm afraid that's one of the worst examples I've seen! To get rid of them you'll need to buy a blower brush and follow this workshop we published earlier: http://www.cameralabs.com/workshops/dslr_dust/
Fortunately it's quite easy to reotuch dust marks from your images using software on your computer, so if you have any shots you're really pleased with, you can 'clean' them by hand.
I'd also say your photo looks like it was taken with a high sensitivity ISO setting - maybe 800 ISO. If the light was low, then this is fine, but if it was bright, then you may have been able to use a smaller ISO number to get a smoother result - like 400 or 200 ISO. But for fast action, you may have to accept using higher ISOs to get a fast enough shutter speed to freeze the motion.
I still think it's a great shot though!