Nice drawings! In order to improve you'll need to spend more time learning the basics, the fundamentals. I recommend to start with basic perspective and how to draw simple geometric forms (spheres, boxes, cylinders). This will give you the basic skill to draw everything else, since everything can be broken down into these simple forms. From there it's a matter of learning what the specific object that you want to draw looks like. There are a lot of good books and tutorials out there on the subject, Like Scott Robertson's How to Draw and Perspective Made Easy by Ernest Norling.
For figure drawing and character design, I recommend the FORCE drawing books by Mike Mattesi. I hope this helps :).
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