Ask your friend how deeply they want to be critiqued. IMO, a true critique (rather than just idle commentary) should be a two-way street and it's much more dangerous when dealing with friends.
Whenever I ask a friend for a crit, I specify what level I want. If they're seeing a first draft as I'm writing it, I ask only for GOOD comments, to keep my motivation up.
Once I've made my own first edit/revision pass, I ask for what I call LION comments -- big picture plot holes and motivation problems. The kinds of things that will require I cut and revise entire scenes or even sections of the work.
After I'm pretty sure it's structurally sound, I do my own MOUSE (line-by-line polish) pass. After that, I get help from an editor friend to help me learn the details of grammar that I'm missing.
I always specify what kind of crit I want, because then? I can't be upset when they give it to me. If I ask for LION stuff and someone tells me they think my MC is weak and weepy in the middle section, I fix it instead of getting my feelings hurt.
Then again, my writing group is old hat at giving and receiving crits, so we've worked out a lot of the kinks.
Not sure if that'll help YOU, but it's definitely the way I consider it my job as a writer when it comes to requesting crits. I respect my critters too much to ask them to hold my ego at the same time.