You wrote a piece. You set it down. You came back to it. Oh my, it sucks so bad you want to hide your head in shame. What to do?
If you never liked making big changes to drafts, you have no choice now: you’ll have to make big changes. So get your head around the fact, so that you don’t end up doing the revision begrudgingly. Otherwise, you could end up just doing a half-assed job.
Determine Why It Sucks
Look at the big picture. Does the main topic seem too banal after the fact? Does the entire discussion feel incomplete? Does the writing make the subject seem uninteresting? Consider all the big picture issues. Most of time, a draft that just reads bad owes its problems to one of those.
What To Do Next
Once you have a clearer idea of what the problem really is, then you can begin formulating a solution. Do note that a solution will likely require multiple paragraph revisions, maybe even cutting entire paragraphs from the draft.
If the problem is just the writing itself, then you should have an easier time compared to those big picture problems. Start with using a grammar software to get suggestions on what parts to change. Then, slowly go over the draft, implementing some good writing basics: keeping one idea per paragraph, using shorter sentences, and so on.