I'm not sure if you have read through this post yet, but cichlidman has a pretty good stickied post in the FW rate my tank forum that gives a lot of good info on how to take a good picture.
Aquatic Photography: A Personal Experience
Personally for closer up pictures of my fish I will have the flash on and put my camera on micro mode (looks like a picture of a flower on my kodak cam) so it will try to focus on closer up objects. Then I will get as close as I can with the fish still in focus and take the picture. You want to make sure that you have your camera at a downward angle so the flash doesn't reflect off the glass right back into your camera's lens.
Once you get a few pictures, put them on your computer and see which ones actually look good on there. This is where you can do a little bit of editing (nobody has to know
). I mentioned before to get as close as you can with the fish still in focus, this doesn't have to be as close as you want your picture to look though. With digital cameras producing much higher quality pictures these days, you should be able to crop the picture down to just the fish and it will appear to be a close up shot of the fish and still be a very clear picture. This has been the trick I have used to get good shots of my fish. Here are a couple examples below of the original shot followed by the cropped version of that same shot.
