I must agree with the previous poster, these are great first images!
My first images were, well, horrendous!
As it has already been said, the exposure is good and so is the sharpness, where you need some work is your composition.
Luckily there are plenty of resources out there to learn!
In the end composition is of course completely up to you, if you like naturalist type pictures, go for it, if you want to take the artistic way thats cool as well, you just have to start thinking about shots before you take them, how you can take a unique and interesting picture of your subject that will make it pop.
Simply google "underwater photography composition" and you will have material enough to read for hours!
I will often draw out a picture of my subject before I even hit the water, if I go in with a specific plan in mind I will get 50% more keepers than when I just jump in and shoot away.
Keep at it, you've got a headstart on a lot of us!
All the best, Morten
- MMPower likes this