I do multiple layers of sketch, actually. The first, which I call the 'Potato' stage, is basically bean and gumdrop-shaped heads and bodies to place where characters are going to go in a panel, and similarly vague lines and shapes for other important elements. I do this with a very light 3H pencil. Once I have those figured out, I place my text bubbles.
The next layer is the loose sketch, where I start figuring out actual anatomy, faces/expressions, buildings, etc. This is messy as hell, and rather like chiseling shapes out of stone. I do this stage with the 3H pencil, too.
Once I've got things looking more or less right, I do the 'clean pencils' stage. I go over the lines I want to keep with a darker HB or B pencil. This helps me figure out what's actually going on with my messy sketch, and whether it actually looks as good as I think it does. This is where any errors become much more obvious, and the whole thing starts looking much better.
Then, and only then, once I have the clean pencils done to my liking, I actually put down ink and finalize my linework. Yes, doing multiple stages is a pain in the ass, but I've noticed if I skip any of them, my art suffers for it.
Have a progression image of one of my old art pieces!