Hi there, welcome to PJ. I realise that you've put a blown up version for the detail to show the dithering, but that's not really needed 'cos the little + and - can do that for you.
If you haven't already, read cure's pixel art guide (especially the dither bits).
Blunt but hopefully constructive crit alert ;)
The best dithering practice begins by questions: must I really dither, and why?
In many cases, the answers are: no, because it turns a piece into a noisy mess.
Wet sharks are shiny, and best rendered by sharp reflections. Waves have more uneven patterns than checkerboards. Hair is either strands, or shiny patches. Sky is... difficult anyway.
This piece is lacking in more fundamental elements: composition, shading, clean lines, contrast and color. These are the basics you should seek to build your art upon. Dithering is an advanced pixelling technique, which demands control at the individual pixel level. This can wait a little!
Anyway, welcome on PJ!
Thanks for your critique. I am a total noob at this for sure so I was hoping to receive pointers from people who are better than me. Thank you, I'll put this to good use.