When I'm trying to work out a front end idea, I'll draw a large collection of front ends. However, I will only add contrast and some details to one side of the sketch. It's a simple trick that forces you to work out a design only from one side; this is important because if your design works well with one side, it will also work well when its mirrored as you finish the rest of the sketch.
This also works with rear views and plan views. It helps to break down design elements and create design depth.