Somethings ive learned is that you gotta look at stuff, look at all of the shapes things have in it, simplify the shapes to like rectangles and triangles and circles so its easy to memorize and replicate, then fill in the details afterwards, and especially for shading look at how light affects things and see if you can recrate it on grayscale or even with color, dont be afraid to start small or use references, and thats about it for general non-specific advice