For the longest time I wasn't the best judge of my work. Granted, I had a general idea of what sucked and what was decent. I was never stupid enough to think anything I wrote was cloud-in-heaven perfect, but when it came to looking at my writing and being able to find out what was wrong, I had a hard time.
Once I joined an online workshop things got much better. Not only was I able to read good information about things to look for when critiquing (I was a natural at critiquing diplomatically), but I got back loads of helpful critiques of my own work pointing out things I had never thought of or ever seen before. At times someone would point out something I still didn't think was a big deal and didn't bother with it (especially if only one person out of say, the twelve, thought so), but I appreciated the comment all the same. But if the majority of those looking at the piece thought something had to be done with such-and-such part, there's a good reason I should look into it more. And usually I would sit there nodding, thinking, "Yeah, I never thought of that, but yeah." So now I have a much better idea of what I'm doing and I think I make much better judgements than before.
When I do critiques I like to keep things light. Even if there is something seriously wrong or that I feel is icky concerning whatever it is I'm reading, I'll let the writer know. That's my job. That's why they've been confident enough to let some stranger read it. But I'm not rude. As I've said, I critique diplomaticlly. I make a few goofy wise-cracks here and there and put in the occasional smiley face and always leave with a positive "Keep at it!" comment. Even if they might be competition for me in the future. But hey, if they get published before me well then that just means they might have better skill and deserve it or I just need to work harder (or both). We're all writers. We should all be pals with our shared passion. I don't mind proofing or editing at all because it helps both the writer and myself. I may come out of the reading with even more ideas on what to look for in my own reading and other things to avoid doing. Remind myself to check for spelling and grammar errors I might overlook normally. Things like that.
Besides, how else am I going to get better if I don't see any of the bumps in the road?