Hello MLA,
You choose a pretty challenging work for your first pixel art piece. Especially if you are not familiar with how to do pixel art it’s always a good idea to start from small pieces. I think the strongest part of your piece ist he idea. While your idea is good your general drawing skill needs work because it's obvious that you are talented, but you lack experience.
Currently your piece is OK as it is, but it lacks very basic things, like an eye level, perspective and form. The other big things which needs a lot of work is your sense of colors and composition.
It’s hard to do big and complicated artwork if you aren’t even able to draw small things in the right way. It’s by far easier to start with simple small things and build on them step by step.
Let’s start with your piece
There are some smaller issues which hit my eyes immediately.
1, 5 – the snake isn’t consistent in diameter. I don’ttalk about the general anatomical sense, but your lines are messed up at 1 and the diameter changes heavily and perspectivically wrong tot he bally plates at „5“
2 – you just added some rocks in the background which look like pasted. This feeling is caused by just adding them straight at the lavaa surface – they don’t contain any form information.
3 – also how the snake winds around the rock lacks form and perspective
4 – the perspective hwo the rock associate with the lava is wrong too
6 – here you have visual tangent between the rock and the serpents body
7 – the sky also lacks color perspective
8 – you have strong problems with jaggy lines and banding
Also your pallet contains lots of similar colors – maybe caused through editing.
But the biggest issue is the lack of forms (perspective)
I just made a pretty fast edit to show you a way how you can solve problems. I would call this a bit more detailled thumbnail sketch - it still has lots of issues I'd need to work on because I recognized them, but for demonstration purposes it's OK. It took "only" 30 minutes. I suppose you worked by far l onger on your piece.
Here is the process:
1 – I lay in the horizont and also some raw bg
2 – I add some colors to define more what I want to do
3 – now I lay in some foreground shape do define the position and composition of the shapes who will change into rocks later on
4 – I start with adding in the snake
5 – now it’s time to play more around with perspective, composition, colors, layering etc etc. to get the best result possible – I don’t played around a lot though and don't fixed the change of the horizont line due to composition. I just proceeded with the usual process.
6 to 8 – Adding more colors, changing stuff, fix all issues occur and always work from the big things to the small things.
8 is where i stopped, I just worked on a bit from 6 to illustrate that you can take it further with adding colors details and stuff.

It’s easy to work on faults if you started just with a drawing, the farther you get in your process the harder it will get to remove those general big problems. Pieces with „big“ issues and lots of details can look nice or even great, but imo it’s not worth to work on anything which issues you recognized and aren’t able to solve without putting in a huge amount of time in them.
The art is to improve your piece continuously (over your whole process) and add always more details just where they are needed. After you refined it to a pretty fine state I’d recommend to add pixel art techniques.
If you aren’t capable of seeing your faults work on your basics - this helps a lot. You can't put enough work in your basics.

Big pieces take serious effort and skill. The bigger the pixel art that more time you need to refine and the more general art issues occur and the more often you have to redraw parts oft he artwork. If you build your piece step by step it’s easy to rescale it in the early steps too, because you haven’t added pixal art technique anywhere which is destroyed by resizing. it nowhere. If I would cut down my edit by half it would still look the same or? And it's by far less work with detailling.
