Give useful feedback. Don’t just praise the writer and not make any kind of useful comments in a manuscript. That isn’t helpful.
Critique groups and partners are meant to help writers grow, not just pat them on the back. You want to be both encouraged and challenged by your group/partner, and encourage and challenge them in return.
Good writers always want to be challenged to improve their writing. Even multi-published, best-selling authors are constantly learning new things about their writing craft to improve and grow.
Listen to the feedback people give you. What’s the point of being in a critique group if you’re not going to listen to anything people tell you?
Be open to hearing things—sometimes hard things—about your writing. Realize that it’s meant to help you become a better writer.
And then do something about the things people tell you. Don’t just smile, nod, and go your merry way. Work to improve your writing and make it better because of the feedback you get.
On the flip side, be judicious about what advice you take or ignore. Not all critique comments are going to be good for the manuscript.
It’s not that your critiquer was wrong, just that the comment isn’t right for your story.
Go with your gut and try to discern what advice you follow, and what advice you choose to ignore. (Just make sure you don’t ignore everything your critique partner/group tells you!)
Your discernment will get better the longer you write and get feedback on your writing. It might be hard at first to figure out what to keep or ignore, but you’ll find it gets easier as you get more and more feedback. You’ll start to recognize what comments are most applicable for your manuscript.
Now you’re ready to dive into your first critique group! Go to it!