It’s a very hard thing to do! Beacuse as much as the one person is wanting to give constructive criticism about the other persons work you never know how some is going to react to be being told about their mistakes.
The thing about constructive criticism is that its meant to be the process of offering valid and well-reasoned opinions about the other persons work. This involves both positive and negative comments, in a friendly manner rather than an oppositional one.
Its not easy to take or except critical commnets about your work though, it took me a long time to get used to having someone look at my work and then pick holes in it, but it is helpful when done in the correct manner by someone you know is judging your work to be helpful.
Like with art, you spend hours creating something you love to then sit there and have to have all the flaws pointed out to you, Its not a reason to give up though, if anything when you know what you have done wrong you can go back and change it and now it looks better.
I have got to the stage now where I can spot mistakes in others work, thats a good and a bad thing. My sister once showed me some art work and asked me what I thought of it! Talk about awkward you see some people show you things but you know they don’t want to know what’s wrong with it they just wanna show it to you.
Well I looked at it and the first thing I wanted to say was “the hands are to small for the body.” But that comment would have gone down like a led balloon so I didnt say anything.
The same went for me when I started to show people my first chapter of my book and some just said nice things and some pointed out all the mistakes but only one friend sat down and said “This would work so much better in first person point of view past tense.” And I thought well I will give this a go, and she was right it does. So I’m in the middle of total rewrite but it has improved it no end.
Sometimes its good to have a friend that has the guts to stand up and risk offending you buy offering constructive criticism.