A critique group—the right critique group—is a wonderful thing, especially for a not-yet-published writer. Meeting regularly, whether in person or by the Internet, will at the very least encourage you to keep turning out pages.
Ideally your critique partners will catch things that you overlooked (why is that character's name Mandy on p. 3 and Mandi on p. 35 and how can her hair be straggling down her back in Chapter 3 when she just had it cut short in Chapter 1, a few weeks previous?)
And then there are the things that you as the writer know but haven't quite communicated. (You may know that Cuthbert's deep silences and curt answers betoken a depth of soul and shrinking from the banalities of crude modern life but your critique partners may point out that he comes across as a jerk.)
Just as it's hard for a writer to proofread her own work—your brain reads the even though your fingers typed teh—having fresh eyes on your work to look for continuity issues and for the overall sense and pace is invaluable.
Of course, there are good critique groups and bad critique groups. You don't want readers who delight in tearing down with no suggestions as to how to fix what they see as wrong. You don't want readers who hate the sort of book you're writing. ("I can't read chick lit" or "I hate sci-fi"—that sort of attitude.) You don't want readers who are fixated on looking for their pet aversions, be it passive voice, the use of “had” or adverbs or semi-colons, to the exclusion of paying attention to the story.
And you really don't want readers who are no more than cheerleaders. "O, I love it! You're an amazing writer." Well, maybe a little cheerleading to keep you plugging away is a good thing. But if you're serious about the writing life, you've got to learn to deal with criticism—you've got to learn to learn from criticism.
If you do cheerlead, at least be specific. “I love the way you described the sound of his gargling” or “The way you show your ninja hero's weakness by having him insist on a night light makes him much more interesting to me” is a lot more useful than “Oh, you're such a good writer.”
In my opinion, a good critique group needs to be small—two to four folks would be plenty, assuming you're going to give good attention to each other's work.
Where to find a critique group? The one I was in before I had a contract and an editor of my own grew out of a writing class I took. Four of us from the class continued to meet after the class had run its course. This is a good way of forming a group because by participating in a class with the other folks, you'll gain a feeling for their critique style and whether it's likely to be useful. I know that several of the classes I've taught have formed spin-off groups.
There are online critique groups but I have no experience with them. Browse around and see what you can find.
Once you are in a critique group, you should be able to judge after a few sessions if it's going to be helpful or not. If it's not, get out. If it's really toxic, get out fast.
Here are a few suggestions for critiquing a novel.
Setting: Is there a strong sense of place? Do we know when and where the action of each scene is taking place? Are most of the senses engaged—do we know what this place smells, sounds, feels like? Is the woolen coat the girl wears rough under the hero's fingers?
And, this is the big question, are the characters acting against the backdrop of setting? “Harold always ate his dinner at the table in the center of the room. It was covered by a red tablecloth with a small burn spot.”
Or are they interacting with the setting? (much better) "Harold carried his microwaved TV dinner to the table in the center of the room. As always, he positioned the plastic dish to cover the burn Matilda's cigar had left in the red tablecloth."
Characters: Are the main characters real, fully developed people with a past? What do they want to achieve? What stands in their way? Are they likable or at least interesting so that readers will want to know what is going to happen to them?
Dialogue: Does the dialogue sound like real people talking? (Hint—most folks in speaking use contractions - "I (would not) wouldn't pick up that ferret if I were you, Cyril.") Do the main characters have distinctive voices? Can the reader keep track of who's speaking?
Show, Don't Tell: Is the author telling the reader things that the characters should be showing the reader?
“Horace was really angry.” That's TELL and it's boring.
“The knuckles on Horace's clenched fist were white but his face was a deep red. Without warning, he smashed his fist through the dry wall.” That's SHOW. See the difference?
Odds and Ends: In my classes, I generally suggest that we not focus on typos, misspellings, punctuation, or grammar. I make these corrections on the hard copy but don't take up time in class with the basics.
I do, however, address the all too common misuse of its/it's and the difference between lie and lay.
And one last tip. I think it's a mistake to critique work on the basis of the author reading aloud. Unless, of course, you're critiquing performance. The thing is, a good reader can make mediocre writing sound better than it is and a bad reader can make great writing sound like…that stuff you step in.