I guess rechecking the basics of anatomy is never a waste of time, but what I really mean is: You check for proportions while drawing anyways, so there will be a natural growth just by practicing.
If you come to a point, where you feel dissatisfied with your style, you can switch it up, either by varying your tools and means, or by looking into special techniques and methods. But that pretty much would have to be an artistic decision following your very own taste. For now, there are no obvious problems with your sketches, so there can't be obvious advice from anyone else. The burden of coming up with problems is all yours, Mr./Mrs. Artist. :D
What you maybe could do is critiquing other artists. Looking at some "beginner" stuff, reflecting on what you would have done differently, and trying to put it into words, can give you a new point of view on your own skills and techniques. And if you see something which gives you the feeling: "Maaan, I wish I could do that", then there is some inspiration for further development right there.