[Ki-Mono]

Starting with the body shape: they are a bit of a squishy bottle. The front is a lop-sided triangle, which then bottles down and rounds out. Since the shape is so vague, I recommend using a couple references to get the hang of it.
The head is mainly covered by the eyeball. It is very large compared to everything else. If you plan to make this into a species, I would recommend really accenting the eyes and maybe making them cartoonishly big. In general the eyes have a pretty "dead" look in real life, but you can give them more life with your style (Side note, but fish also don't have eye lids, but if you go for a more cartoonish look don't worry about it too much). The gills are located behind the eyes, not under them. They are also what I would call the end of the head area. The mouth is surprisingly easy. All you're gonna do is draw a little "slit" near the top of the head. Adding a little bottle lip will help it look better.
Lastly I would just take better care of the fin placement. If you study photos, you will notice the fins attach right where the body starts to bottle down; and usually only attaches at a single place where it then begins to "fan out".
Back tail fins vary in lots of shapes and sizes. Mostly they are either round or triangle shaped. If you plan to make this a species, having fun with all types of tail color and shapes is a recommendation.

Good luck!

ref

[Undyne7119]

thank you, i like it so far!