I don't know much about your camera so I can only give you general help. First, you have to stop the movement in your tank so shutting off powerheads and filters is usually a good idea. Second, setting your camera to the lowest ISO helps get a less grainy picture. Third, if you can shoot in RAW format that will help deal with white balance problems so you can fix it in post processing. Forth, shoot with a tripod to lessen the chances of shake (blur). Fifth, focus on they eyes of fish. Six, go for creative angles but usually not more than 45 degrees due to the distortion glass/acrylic can cause.
You can add light to the tank by placing lamps on the sides but make sure they are at least 6300K bulbs (GE 6300K bulbs can usually be found at Wal-Mart). Amazingly, tank lights are not bright enough to get really high shutter speeds! You should also turn off the room lights to avoid glare and mixing lighting types which confuses some camera's auto white balance.
Hope that helps. If you want specific help don't hesitate asking.