I saw there was a trend on breakthrough drawing tips or ways of thinking going around, so here's my contribution! There's actually so many big and small things that I can pinpoint my learning back to, but laying in your key light like this and thinking about forms in simplified shapes is probably the first one I would share. Once you block in your key light, you know that any other light illuminating the form is going to be bounce light, fill light, specularity, etc. and I almost always start rendering with laying in my light over dark shapes unless I know most of the form is going to be lit.