First some don'ts.
Don't join a group that does not like the genre you write.
Don't join a group that changes every line you write.
Don't join a group that want to change the plot and theme of your story.
Don't join a group the wants to change your characters and your ending.
So much for the don'ts. Look for a group that does the following:
Mentions inconsistencies in your story. (I can't believe the number of times I've changed the color of hair of a character.)
Mentions motivation of character.
Mentions clearness of sentences and awkward sentences.
Mentions emotions, reflections and inner thoughts of characters. Are they consistent with the character? GMC
Mentions POV. Do you head hop within scenes?
Mentions too much telling and not enough showing.
Mentions too much passive voice.
Mentions strength or weakness of ending of story.
Reads or writes books in the genre you are writing.
A member in one group I belonged to was so severe in her criticisms I almost gave up writing. Thankfully, I did not since I've had four books published, and I'm in the process of final editing before sending out a proposal to an editor about my latest book. Thanks to the critique group I belong to now, I am a better writer.