While I'd really like to be able to do that some day, I'm not there yet. I have to go through a process by putting something really rough down and then working with it. Kind of as if I were sculpting, roughing out a basic form in clay and then adding, subtracting, and pushing things around on top of that initial rough shape until it is gradually honed into a finished piece. I don't know how many other people can relate to this way of working, but I feel like I see this process in the work of Chuck Jones.
Of course Chuck Jones' roughs are beautiful, because he drew with such a natural sense of appeal. But look at how rough these frogs are from his "One Froggy Evening" short:


Cleaning up a final drawing has always been a tough thing for me, so I've been tending to try and make it perfect in the rough and as a consequence wasting too much time on it. We can't all be Alex Toth unfortunately, some of us are actually human. As good as Chuck Jones was, I think he was human too, or at least I can relate to the way he seems to draw a lot more. If you get hung up with the clean-up phase like I do, these drawings show how Jones did it, so maybe we can all learn something from them.
The real point of this post though, is that it's okay to go rough, and just leave it. Look at how rough Jones went here, they're almost more a series of indications than they are drawings. We can always go back and do another pass to clean it up and clarify it later. The important thing is to get the idea out.