When I first joined a crit group, I thought it would be simple as pie, we'd exchange chapters, discuss, and be happy wonderful writers! Rainbows and cookies would fall from the sky!
I have, of course, learned much, much more. I've noticed in my recent revisions, however, that I've learned some great stuff about revising from my crit groups, too, completely by accident.
Spotting Trouble: People used to tell me that something didn't work in my writing, and I didn't get it. It was soooo much easier to spot it in other people's writing than in my own. But having done the crit group thing for almost a year now, I've realized better what I've done wrong in my writing, and I'm quicker to spot my own mistakes.
Understanding Trouble: Those writerly things that people said, you know, about ambiguous stuff like voice and pace and point of view...I didn't get that. But when I noticed it in other people's work and made a comment on it, and then someone made the exact same comment about a passage in my work...well, it makes sense now.
Revision Method: My super-awesome writing group, The Wunderkin, makes comments using the Comment function in word. Say you're reading text from your group, and you think something needs description. You just highlight the text and add a comment, and then the text is now highlighted in a bright color and has a little balloon trailing off it so you can write your own comment or question. It's simple as pie, and so much easier to read than changing the color of text or making line notes like "such-and-such needs work on line 23 of page 4" (at least imo). In MS Word on PCs (doesn't work like this on Macs), just hit ctrl+alt+m and a fancy comment box shows up!
This is something we do when we pass around files, but it's something that I've started doing in my own work. As I'm reading through my pages, I may notice a quick-fix: just rearrange a sentence or cut a paragraph and it's better. Or, I might notice something that might a hardy fix: my characters say they meet on Wednesday, but didn't I say in Chapter 4 it was Tuesday? I put this sentence here to foreshadow something later, but then the book went in a different direction. Do I explain how this bit of magic works here, or later?
For these kind of fixes, those that will take a lot of thought and usually flipping between pages and chapters, I've started to just make a comment with Word's comment function. All I do is hit ctrl+alt+m and make myself a little note: check dates later; add scene about this in Chapter 10; compare this paragraph to the one after the character do x. That sort of thing. Then, when I do my final read-through, I can easily change dates or swap scenes... and I haven't lost the momentum of reading through tedious back-tracking.