You will be surprised how turbid the water is unless you have absolute crystal clear water.
The water will get clearer towards the surface of the water column.
Try shooting in as much light as possible.
Keep camera steady underwater by making some prop, but make sure it doesn't float away!!
A steady shot will look much more professional.
I use 1.1 metre long selfie stick that telescopes down to about 15 cm, which means that you can keep it attached to the camera without difficulty. If you set the self timer to 10 seconds you have time to get the subject lined up. For photographing flies I find it easier to fix the rod and take the camera to the fly.