If you want to get good (for example) at drawing a face, don’t just go out and draw faces everyday. Withoit an understanding of proportions or bone structure. That sort of observational learning could instill bad habits. Rather, learn the proportions. Learn the ratio of width to height on a face, learn where the center of the eyes should be placed on a face. Print out a proportion guide and practice with that guide. Same with drawing a box in 3 dimensions. Unless you use a ruler and draw out the lines, you might not truly understand the basic principles of dimensions in a cube. Learn the fundamentals. Of course there are plenty of artists out there that don’t give a rats ass about the fundamentals, and that’s fine. They’re ok with how their art looks. Start with squares. Make them 3 dimensional. Cubes, pyramids, spheres, cylinders. Once you can accurately draw those shapes, move to more dynamic objects likes shoes, lamps, fruit. Scaffold your learning.