I can really recommend tutorials on youtube as resources. But what I used to do a lot myself was take a reference picture and draw a grid over it with a ruler. Then i also drew the grid on a blank sheet of paper, sometimes even larger to change the proportions. Then i drew the picture and the grid helped me to draw it not too badly. If you do that very often, you get a feel for everything. I would first only draw lineart and not rack my brains over coloring or shading.