Rate my skill level

[xelfereht]

Look this art thing is hard for anyone and your appeal to improve is at least commendable.
Like I've previously suggested, here is a way to attain a high degree of clarity about your direction and what skills you need to improve.

step one.

gather a bunch of work maybe 50 pieces of art by artists you admire
pieces that also relate thematically with your interests as well as the work applications you foresee being interest in.
for example, historical fantasy / character concepts.

build a portfolio out of the best work you can find, a dream portfolio.

step two.

replace all those images with your own. push your images till they can comfortably stand along side the mock port folio you made.

as easy and hard as that.
but the clarity of where your'e trying to go will make things a ton smoother.

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Your sketchbook at the moment reveals a severe lack of direction, a few decent studies but in service of nothing. A minimal level of execution is where every piece ends.

You have to push your images more if you want the quality to raise
you have the hit the next level of quality once before you can do it consistently.
sometimes this means spending a 100+ hours on a single image struggling through till you can say it's your best yet.

do the mock up portfolio, if you have questions or need help with it, welcome to ask.
if you find excuses to dismiss the idea, then good luck is all I'll have to say