I'm not gonna post because artblock and- sorry, I will post something when I will ca but rn I just want to shoot myself when I open my sketchbook
Value (how dark or light) and contrast (difference between two values)
Positive space (what your object is) and negative space (everything else)
Shading of 5 Basic Geometric Shapes, with light source in top left
https://www.piskelapp.com/p/agxzfnBpc2tlbC1hcHByEwsSBlBpc2tlbBiAgOCwhbe5Cww/view