This was my sketch for a Schell Games Art Challenge, where the goal was to take your two favorite comic and/or cartoon characters and fuse them together - hence Iron Man and Spider Man combining to create . . . The Iron Spider!
When I paint or sketch, I typically start with one of 2 methods: 2-3 tone blocked in shapes like this piece, or just straight up linear. Or sometimes if I'm feeling magnanimous I'll allow myself to work with a combination of the 2. I guess that'd technically be a 3rd method I sometimes paint with :P