If you want to get really good diving photos:
1. Go to a dive site with good visibility
2. Make sure it's sunny up top so the light's good
3. Find some wonderfully coloured coral
4. Add some beautiful tropical fish
5. Delete the disappointingly dull photos taken with your GoPro like this one:
6. Go with someone who has a decent camera and borrow their photos!
Adam on Bravo has a good waterproof housing and strobe light for his camera so have a look here