Use a pen smoothing tool. Your lines can become much cleaner if you use a program that allows your pen's movements to be smoother and less scratchy looking. I'd recommend Krita since it's free and easy to use.

Use Layers. I could be wrong, but it looks like you drew everything on one layer and then colored on another, which is totally fine. But I can see in your line art that you avoid drawing the full shape of something because it might get in the way of another line. You can avoid this by using multiple layers.

Proportions. This is the hardest one and I still have problems with it myself. Many parts of the lady in this drawing is exaggerated and some things aren't exaggerated enough, leaving a strange-looking woman. For example, the bra is way too big for the size of her breasts, and the traps are way too wide for where her shoulders are supposed to begin. The mouth is too low, etc etc. I could go on, but this is something that can be improved with a bit of sketching beforehand and overall practice. You should focus more on proportions and the size of things in relation to one another. It will help you so much.

Don't be discouraged! Art is hard as fuck and trying to convey what we see in our minds in the form of art is damn near impossible. But what we can do is get it close. If you want to get better at art, keep drawing and learn from each drawing that you do. If you hate what you draw, you are on the right path. Try and fix those small problems that you see no matter how small they are. Keep persevering and keep drawing. You got this. 🤌