Although not specifically geared towards the underwater photographer, certain tips hold true for all wildlife photography and especially contest photography.
The BBC published this list and accompanying slideshow in concert with the deadline for the 2013 Wildlife Photographer of the Year Competition approaching. All UW Photogs should take heed of their words of wisdom - or just look at the pretty pictures. To view the tips and sideshows, visit their site.
Canon 15mm f2.8 Fisheye
Canon 5D Mark III
Sea & Sea YS-D1