The first is picture i have chosen is this lionfish, i think the main problem with this shot was that the white balance was incorrectly set and lack of a flash diffuser (which i lost on my 1st day)

Second photo is a Ruppell’s wart slug , due to the flash diffuser being lost and the flash omly lighting up half of the photo i illuminated this using a LED dive torch hehe.

They were both shot at ISO 200, i have also adjusted the curves in photoshop

In the first photo, even though with white balance the image culd have come out of the camera with better colours I would say to think about the composition and framing more first. You can post process the image quite easily in Photoshop to get better colours. I took 5 seconds with it just doing Auto colours, levels, brightness / contrast .. to show you what I mean. The thing that bothers me the most is that thre is only half a lion fish in the photo. And the downward angle does not help either. I would like to see the blue water and some reef in the image not sand. Patience .. the fish will move to a better location !

The second image, even though you said you lit it with a flash light .. it seems over exposed in some areas, and the areas you think are not lit are much better. If something is over exposed you can do nothing to it to correct afterwards, where as underexposed (as long as not black) can be rescued to a certain extent .. white in a digital image = no information.

That being said, good effort, just work on your compositins a bit more, try to immitate other photos you have seen and think are amazing. As you get the composition right the rest will become easier as a well composed image just needs the right settings on the camera and strobe then !