Like was posted earlier
1. Keep the flash off
2. Try to take your pictures when the rest of the room is dark to reduce reflections and glare.
3. Use the Macro mode on your camera
4. Don't worry about trying to zoom in on the corals most P&S cameras won't allow you to zoom in and stay in focus. If you want to enlarge the coral in the picture use a program to crop the photo (Photoshop elements is an awesome program and is not extremely expensive about $80).
5. Turn all of your pumps off.
6. Make sure your glass is clean inside and outside,
7. If you have micro bubbles wait 10 minutes or so after you turn the pumps off to let the bubbles rise to the surface.
8. Use a tripod if you don't have one set the camera on a solid surface. You can sometimes get away with placing the camera against the glass to help steady the camera but you still have to be very steady.
9. Use a higher ISO rating (this is a tradeoff you lose picture quality and increased grain in your pictures for increased shutter speeds so you can stop the motion, experiment and decide which ISO gives you the best results.)
10. For shy fish use a tripod and set it up several feet from your aquarium and be patient you can also try feeding to lure them out.
11. Take lots of pictures while you have everything set up I usually take a couple hundred pictures everytime I take pictures of my tank and then weed out the 180 bad ones and keep the 20 good ones.
12. Good luck
What model is your camera? Might be able to help with settings if you give me that.