Looking for ways to improve my illustration skills. Does anyone have advice on the areas I should improve on? https://e621.net/posts?tags=sk8th

You're a pretty good artist and there's not much that I dislike about your art.
To me, it's kind of hard to judge what your current level is at. Some of your art seems amateurish, with faces that don't look lined up, body parts that don't match, very little shading and thick black lines. But then I see pieces like this which is pretty dang good!
The shading on your 2D cartoony art is pretty good and matches the style you're going for. I guess the only thing I would like to see, is on your more detailed artwork, such as the one I already mentioned, you could progress your shading to make it look more detailed and realistic. But I guarantee with time you'd be able to achieve it, just by your skills advancing alone.
Great job!