Thank you!+just a dott
Yes, line stabilizing also happen with time, practise and confidence. You don't need really to care about it while beginning, it's really something that come alone with time. A friend of mine one day found a good comparison to it ( but probably a gore one xD ) he said it's probably like a butcher cuting the meat at precise point on the anatomy of the piece of meat he's cutting. I'm sure everyone saw this type of fluid and perfect movement where the meat, bones etc, all split perfectly with a single knife stroke. Often the public wonder what type of knife they use to cut so well. :D It's because there is a knownledge under it ; before even cutting with the knife, the butcher knows how his movement will perform.
For lines, it's a bit the same process ; with time knowing a basic anatomy, perspective and volumes, it feels like 'underlining' a ghost appearing on the paper and shaping it. I don't even think of the line quality , it's just a by-product of trying to do the right move.
So, all in all to say, don't really mind for the line quality ( smooth, thin, etc... ) , but mind for the 'right' placement of it to represent and shape the volume. Even if line shakes , or has many little lines it's ok. Subject and what you have to tell is prior to technic. :)