nice colorful pictures !
about improvement, it would be good to know what is the direction you wanna take your career so we can give more specific advises
I see female only pinup portraits so far but I dont wanna assume anything based on that since your needs and taste can be completely different from your current work
regardles your future goals, there are lots of things you can work on now. It seems like you have a sense for design and gesture to express personality, but you lack understanding at fundamentals. You also use established characters and archetypes with rendering shortcuts to solve problems you cant handle yet. Aiming for a finished illustration is not a bad thing at all, but you also need to keep in mind that illustration as a genre has the most problems to solve and takes the longest time to master.
here is my list to start with:
anatomy: crucial to understand form and structure, there are very good free or cheap resources you can find online, all you need to do is practice daily.
some resources. Proko on youtube, Andrew Loomis books, Michael Hampton- design and invention, Anatomy for sculptors, Bridgman's Complete Guide To Drawing From Life, Burne Hogarth - Drawing Dynamic Hands, Steve Huston - new masters academy online courses
colors / painting : as exciting as they are, unfortunately colors are only the last step in the whole workflow, it's more important to establish good values and composition. for basics I highly recommend any video from CTRL + Paint . for advanced coloring there is a book called James Gurney - Color and light. Advanced Lighting course by Sam Nielson on schoolism is a well designed online class with homework, covering literally everything you need to know to have control over your colors. also painting from life will answer many of your questions when you get stuck
style: now this one is a bit tricky, because it's very charming, most of the times style is what we fall in love with first, but its the result of years of development and a simplified version of reality. meaning to make it work you need to have a higher understanding and need to know what's outside the style. so when starting out you gotta let that style thing go and focus on understanding how things work
second thought on the topic, as brush work is a huge part of your style and that's something you mainly steal /learn from other artists. I recommend to learn from more artists, including old masters, not just one. I can discover traces of sakimichan's rendering technique, but with that you also copied her mistakes, you need to aim higher in quality/ experience when it comes to learning from others. that's the main reason its just wiser to use old masters to study from.
storytelling: start making personal content. fanarts are great for rendering practice, because you already have the brief/ design problems solved, but you should aim for a balance between practice and exploration
studies: some things like anatomy you gotta practice as often as you can, because it takes time to learn, but many things like composition and textures you should study with application, so gather references for every image you work on and commit to the problems until you figure them out
one more useful advice, draw on paper with pen, it's gonna force you to make decisions and develop confidence
also keep posting, dedication pays off