I'll be the 3rd person to recommend Understanding comics. It is required reading.
The big thing is practice. Practice. Practice. Then go practice. I've been working kinda on comics for a while and sometimes, I can churn out a panel like nobodies buisness. The pose aligns just right and its super easy. Other times, a single panel takes me hours, because I keep finding I'm doing it wrong.
But you know what? the next time I do a scene like that, I do it a bit faster. I rarely go online to find references. Instead, I stand up from my pen and paper, and make whatever stupid pose I'm trying to draw and mentally take inventory of where all my limbs are, how my body looks and feels. A mirror may help.
In regards to asking the artist, a quick google claims that
This book has includes an extensive interview with creator Masashi Kishimoto, step-by-step details on the process of creating a Naruto illustration, 20 pages of notes from the author about each image in the book and a beautiful double-sided poster!
That might be worth checking out.
About how many drafts would you guys predict that it took that whole comic, and what sorts of panels would you all say take more drafts to perfect than others?
That's a really hard thing to guess, because of what goes into the comic. there are 3 steps in my mind that might count as 'drafts.' 1st, the overarching story. The script to that was probably passed through a few editing hands before any art got started. It really depends on the project on how much script you should have. I've been focusing on just the next strip on my current stuff. I have notebooks with outlines for twenty odd chapters for other stories that can't see the light of day until i finish rewriting them.
(I saw a comment here recommending to find scripts and try drawing the first few pages, then compare work. I'm so gonna do that!)
2nd. the page itself. Panel layout, camera angles, action poses, there is SO MUCH that goes into each page, I can't do it justice. A lot of good books have been suggested, so check out those. Duck into a bookstore and see what they have. I have fond memories of draw comics the marvel way! and I love How to make webcomics
I do end up drawing and redrawing the pencils several times, before I ink it.
3rd, you'd be surprised how much rewriting can go into every line of dialogue. For me at least. I write what I want to say, then I remove every word I can get away with, then I have to cram it inside of a bubble. Sometimes, writing a sentence takes longer then drawing a panel!
Closing remarks: I have 2 final pieces of advice: 1st: Invent your own process. Figure out how you want to do it. Each of us is shaped by our environment, by our upbringing, by the books we've read, by the artists we admire. And then, none of us have exactly the same tools. Make a process that works for you. (Start making. And then, when you're comfortable, experiment! I recently bought a calligraphy dip pen and have been using that for my inking. For so long, I had thought it an outdated piece of technology, but now I love it so much! but you don't need one. I did a lot of comics with paper and a ball point pen. They weren't pretty, but they were mine.)
Finally, (because I doubt you're even reading this far down!) practice does not necessarily equal practice. All the anatomy lessons, perspective practice, the realistic images, those are good fundamentals. I wish I had them. But if you want to learn to make comics, come up with a story, not too long of one, and draw it. Play with what you can do. Learn to tell a story. And, ya know, you'l get to a point where you need a cool city scene, and all that perspective practice flows into the panel. Or you'll want to emphasize how beautiful your villainess is, and your anatomy floods down your pen. Everything you learn is a tool in your toolbox and the fundamentals are very useful, although they don't seem to be, they are part of the path.
TLDR: Confucius say: Make some comics. They you will know how to make them. Also, read books.