This is a solid start. Make sure you are practicing throwing straight lines in your warm-up practices. I do at least 5 minutes or one screen at the start of any formal art session of straight lines, s-curves, c-curves, circles, and sometimes ellipses. Those things alone will make your drawings better.
These types of exercises are designed to get you thinking about objects as 3D forms and work through visualizing the whole thing. Part of this you will get to when studying perspective, but you can benefit now by lightly drawing the hidden faces of objects. Then make sure that your lines are parallel, if they are going the same direction. There's a good bit of wobble to your lines and segmentation that will clear up if you practice making quick stroked straight lines. Drawing through the sphere will also help you see issues with those, but I will say subtracting from spheres can be quite complex because you have to consider not only the form of the sphere, but what shape the cutting tool would leave behind.
Using something like Blender with wireframe mode on will help with this a lot. But more than anything else, just keep practicing and work towards improvement.
