If using a DSLR, get yourself a rubber lens hood for those up against the glass shots.B. Carefully press the camera lens on the aquarium glass. Be careful to not scratch the glass. Hold the camera firmly while taking the picture.
C. If there is no way to press the camera lens to the glass try to carefully rest at least part of the camera on the glass or part of the hand that is holding the camera.
Second that. Holding your breath is one of the most common mistakes people make. It may seem to work during the first couple of shots, but try fifty or a hundred.Instead of holding your breath completely (Meaning a full breath), take a breath and exhale half. Hold your breath at this point. It's actually a less stressed state of being and will allow you to be more comfortable and more steady.