It's a good question, Anon. I honestly don't think that anyone can really perfect it, just become more and more competent and confidant. As to how long it will take to become competent, it depends on how you practice. Don't just mindlessly repeat in variations. Personally, (and no I'm not going to pmw as I refuse to have my work be even remotely associated with this wretched fucking site) drawing mindfully and concisely was the trick. And again, this is just what I've done to gain line consistency and confidence; I'd draw a horizontal across a piece of paper (I bought a couple packs of 500 sheet printer paper and a clipboard to not feel reluctant about wasting resources) then trace that line to the best of my ability several times. Then draw another a set distance below it tracing it again and again. I repeated this until the page was effectively lined, then rotate it 90 degrees and do the same thing until I had a grid. Then I'd trace out with my arm, a circle within eat square, trying to make it touch all 4 sides without going over or not actually touching. Tracing with motion before actually making the line helps tremendously and finding the balance of speed and control is essential. I'd fill up that page, turn it over, then do it again. Intermittently varying the size of the squares and by relation, the circles or ellipses.
I filled roughly 1,500 pages in just under a year and noticed an IMMENSE improvement to my line work. It's really about focusing and maintaining mindfulness as to what it is you're trying to accomplish. I'm no professional (yet) and not a teacher so take this advise as you would from a random dude on the internet.
Not a shill, but Peter Han's dynamic stuff does pretty well convey what I mean and have done.>>4448294
Those top ellipses aren't bad. Just try to put down a line and leave it. You can't correct a line by drawing over it. Instead, realize what it is that looks off and do it again while mindfully trying to correct it.