Used some 3D renders to make the buildings right. It's so hard to draw cylinders! 3D is great for stiff elements like buildings, weapons, etc but for characters, I don't recommend them but they are great to determine where highlights will hit. I also use photos of myself or my toys in the same angle/pose but I won't share that because I look stupid. XD
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I guess the most important advice I can give is to study the basics like anatomy, perspective, color and light, etc. I know it's a bit boring so I also recommend doing studies of photos, artworks, movie screenshots, etc. What I mean by doing studies is to copy a picture by painting it from scratch. If you do this again and again, your visual library will increase and you will memorize how to make things.