I would add something to the floor like a pattern to indicate an interior space because the ''tree'' like element goes agains't the idea that this is taking place in a indoor space.Also the empty nature of the space doesn't help establish and interior.
The problem with your light is atleast to me that you did not take a bold approch that use contrast.This look like a overcast day which can work for more melancolic or sad mood.
Alot of time was spend on small detail where thinkimg about the scale of thing would have help create more dynamism by planning .This would have given you the opportunity to establish visual importance in term of scale.
You can certainly imply a large monster without the need to have the whole creature frame inside the composition which can complicate using space in the composition that could be use by other element to establish more context to the scene.
It probably wrong of me to say since there always opportunity to learn in critic but really if you struggle to me it a question of how many fundamental you mix and were your current understanding is and what what level of awareness of your observational skill are.If you would deal with different fundamental using a thumbnail approach instead of trying to work all those thing all at once you could take a big problem and approch it in a more manageable way.
For example thumbnail for gesture,thumbnail for light direction, thumbnail for the interior layout, thumbnail for the creature design, thumbnail to explore the time of the day,etc.It up to you to see what fundamental would benefit from a thumbnalling and since this create a palette of opinion is certainly going to help you avoid working with the first solution you come up with that not always the most harmonious well thought out idea.
This is approch is what i would call thinking a head in a multi stage problem solution fashion obviously there is an order to this process since you want the subject matter to be establish before the color and light are decided but that just how i think.The problem is that often such approch flatten thing because solution are develop independant of each other.So being aware of what wasn't in a scene and now is affecting a scene is important so that the whole can make sense.
I personally think of thumbnail a serie of thumbnail ''trial and error where you must select piece that you must assemble into a ''puzzle''once thing start to make sense.The important thing is to be able to assemble those piece following the fundamental. If you do thing you never study for and try to bring it to something you want to call finish it require a complex understanding of how to pull it out. Practicing honesty with yourself as to what new and what you feel comfortable doing with your current skill can make the difference between a hit or miss yes there is a possibility that you need to do some prepatory study before attempting something big(or more finish if you prefer). Like an athlete it would not be really advice to go play a big game without some stretching and good quantity of game practice before.
You can learn more about the importance of thumb nailing aswell as some trick that can help speed up the process
https://www.youtube.com/watch?v=LREZ2dSTZLQ
The problem remain that to often we try to fix something to the best of were ability because we think more rendering will fix it. The truth is that a strong planning is often gonna make up for a poor rendering. But strong rendering won't make up for poor planning.
There is such as thing as to much planning but confidence is built through practice and project that respect your current skill set.If you do project that are just to far ahead in term of fundamental skill they require it kind of a disservice because you get burn out and get caught up by technicality in your understanding so understanding why you mess up is more important then messing up because unless someone point why something is wrong you won't understand because you leak the mean to understand in the first place.
For example i could say this cast shadow is wrong explain you why it wrong but if you don't understand the principle behind why it wrong it going be a miss opportunity to understand what i was saying.We all make mistake but we should not lean on error to learn how to avoid them. We should lean on were understanding of the nature of the ''error'' obtain through the study of the master and why taking one decision over an other would achieve something closer to were goal and how to correct the direction before it become to committed and harder to change direction.Critic are nice at the end of a piece but they can't save a piece they are more about figuring out where you didn't follow throught in your plan or where you have blind spot in your fundamental.You want most of the critic to be in the thumbnailling and goal setting stage to stay flexible and to clearly define your goal.
Some people might do a paint over they are not necessarily giving you the reason of everything they did but you might wonder why the paint over is more successful.It not always about there rendering skill sometime it there composition choose color choose etc
I am confident that your in the right direction you are already using some form of self critic but remember that self critic is something that is a double edge sword it should be practice but the critic is as good as the person who give it so as you learn specially in the early years listen more than self critic.
When you do project you better to be clear about your intension or the advise might not bring you closer to your goal and would instead bring there vision to life instead it doesn't mean people can't give you better idea it just that you should sometime stick to your goun for the sake of achieving what you had in mind regardless if it better just because it important to reach were objective and not necessarly derail from them you don't always have the freedom to take different route sometime you gotta go all in.
Student don't rely on themselves to correct there homework because the ''answers'' is not the knowledge and an understand of the process to get to the ''answers''. A copy machine is not a thinker. Copying doesn't give you an understanding of a subject.
Before i finish if you feel stuck or if you need some trained eye for a second opinion you should ask for it. Just be aware of how much you are relying on critic and people opinion you can certainly achieve alot by yourselve but you should not be limited by what you know or what they know it why it important to learn from professional always because you don't know the quality of a critic until you master a subject or you do know better and i tell yourself ''i know better'' is a dangerous term because it not always true.Surprisingly sometime artist have a great theorical fundamental understand but keeping track of the fundamental interaction prove to be difficult is an other ball game.Let take the example of riding a bike you might know how to sit where the pedal are the function the break are .But you leak coordination,you don't understand acceleration or how to balance yourself.What i am saying is that there what we know and what we learn by doing.
So you should come back to those who you know are an ''authority'' on the subject.The internet is full of different level of artist so always be open but be careful to who you listen to but not to quick to judge.
Know the rule before you break them.