1. Plenty of light: The more the better, tank lights or top-down flash light all help. Lighting is the key toward good aquarium photography (actually, apply to all photography cases).
2. Faster shutter speed: 1/100s and faster is safer, and 1/200s is nearly OK for turning around bichirs.
3. Smaller aperture size (the larger number): 11 or above (the smaller aperture the larger depth of field).
4. Top-down external flash light on tank top is good (studio flash light is even better), built-in flash light is not good.
5. Be patient, and spend more time (you'll get reward).
I mostly use 1/200s~1/250s, F16~22 for aquarium photography (I do setup plenty of lights for the tank)