I started participating in critique groups last June, so it's been about eight months now. At first I was nervous, afraid I'd say the wrong thing, but all of the groups have been encouraging and useful. For me the process is just as much about learning how to think critically about other people's work as it is my own.
Over time I have gotten better at seeing the flaws in my work sooner, and I'm grateful for that. Even if I still have a way to go.
A book that's recently helped me think more deeply about story structure, and one I can't recommend highly enough, is:
Damon Knight's Creating Short Fiction
It's one of the only how-to-write books I've read cover-to-cover. And it's incredibly useful, with exercises you can immediately apply to your own writing. This is not a fluffy motivational text. It has meat and bones.
The author, Damon Knight (To Serve Man) taught at Clarion for 27 years with his author-wife, Kate Wilhelm, who penned a fantasic writing text herself: Storyteller: Writing Lessons and More from 27 Years of the Clarion Writers' Workshop. In fact, I read her book first and was immediately impressed. It wasn't until later I realized she was the same Kate Wilhelm who wrote Where Late The Sweet Birds Sang, which I'd read years ago and enjoyed.
To sum up: if you're in the market for some book learnin', check these out. You know, if you want. No pressure.