A readable silhouette
My favourite technique for generating many concepts quickly is to use silhouettes. I don’t use this for the important characters such as heroes because I think pure line drawing is more appropriate, but for secondary characters it’s a great technique. I use photobashing for my rough designs and then tweak them to achieve clean silhouettes. Once I’m satisfied they read well and are interesting as an ensemble, I start resolving the designs with line on top.