This certainly was true of me as an undergraduate, and even as a graduate student. My writing practice in most of my undergraduate and graduate coursework was fairly straightforward: think about the paper topic (attend class, read critical articles), write some notes/an outline/select quotes, then whip up a 10-20 page paper in relatively little time. After I'd written the paper, proofreading/tinkering as I went, that was basically it. I'd occasionally read the paper aloud to catch stray grammatical errors, or ask a friend to proofread. But once it was written it was usually done. Only once or twice did I substantially revised a paper I'd already written in full, and it didn't substantially shift my typical writing practice.
For a long time it worked out just fine. And some of these practices were good ones to develop, practices I still undertake, when I'm thinking about and discovering new ideas. But as an undergraduate and new graduate student, I was a pretty novice writer and thinker. Since the end of my MA and into my PhD, I've had to radically shift the way I think about what it means to write, and a big part of that has been learning to revise. After I've finished drafting papers, I've drafted them again (for conferences), and again (for submission-ready publications), and again (for revise-and-resubmits), and again (for dissertation chapters). I'm finally starting to gain a lived sense of what it means to genuinely revise, particularly for long and complex writing (ie: the dissertation).
As I've begun to approach revising my first bit of really complex revising--the first section of my dissertation, a chapter of about 60 pages--I've learned, through trial and error, what really seems to work for me.
Here are the steps I take when revising a longer piece of work:
1. Print: Produce a (double-sided) paper copy of the draft. I'm not quite sure why exactly it took me so long to realize this simple but very important element of the revision process. For a long time I tried to do all my editing on my computer, but eventually I realized it just wasn't working. It was difficult to scroll between pages, I could only see a narrow window of text, and I was finding it hard to conceptualized how all my ideas connected. Once I printed out a paper copy, the process became MUCH easier. Perhaps in part because it is hard to be distracted by social media when staring at a piece of paper.
2. Highlight: Once I printed out a paper copy, I went through and highlighted all the big points I was trying to make in my chapter. Thesis sentence, topic sentences, any central idea that I knew was important to carry through the chapter. This helped me focus on the main points, and make sure I was drawing my ideas through to a conclusion.
3. Write in the Margins: After highlighting the important bits, I went through and basically marked up my entire draft, fixing typos, adding sentences, filling in extra info where my supervisor had asked for more background information or explanation, and making sure my central idea and contribution was carried through my various points. I added transition sentences, did background research on the history of a particular society, and did some significant thinking, but all on physical paper.
4. New Word Docs: I usually work in Scrivener at the beginning of a project (and sometimes all the way through), but this time I found it easier to work with a blank Word screen, probably because I was overwhelmed by the amounts of writing I'd already produced. Opening a blank Word doc worked to help me produce those extra paragraphs and sections I wanted to add without being distracted by the whole.
5. Combine paper and Word drafts into a single whole: this is the fun part! It doesn't take too much time either. Compile all the changes you've made into a single draft. It's enormously satisfying.
A Final Tip:
6. Realize IT TAKES TIME: Genuine revision of ideas takes an enormous amount of thinking time, and it doesn't really work to push it to go faster. Recognize that this kind of hard thinking and writing can be exhausting, and don't try to push yourself beyond what you can do. I realized I had to say no to writing in the evenings after a long day of writing, even though I felt like I shouldn't. Pushing yourself like this doesn't actually work: it makes that work of thinking harder in the long run. You need to give yourself the time and space to do this hard work of thinking, and then the time to recover. Give your brain a well-deserved break, so you can approach the work with fresh eyes again the next day.