Off to a good start !!
I would second everything said above. The “Drawing Ideas” book is one I just read last week and had a huge impact on the way I sketch, but I don’t think I would’ve digested all the information when I was just starting out.
Practicing primitive shapes, both in 2D and in perspective, will be a big help. I still sketch a page full of circles if it’s been a couple days between sketches.
For quick improvement I’d suggest doing an overlay of your shoe sketch, without the “fuzzy” lines. Use long and overlapping strokes, rely on pen pressure to get different line weights.
Cars are tough - there are so many compound curves and volumes that it’s hard to convey it all cohesively. Try making a rough car shape out of primitives (cube, rectangles, cylinders) to get the proportions right.
Good luck!!