A big issue I see a lot of is that as soon as you offer any form of advice, they put up the defensive wall and take it as an insult. Ask them to cast a single different spell one time? They fly off the handle and cuss you out. Ask a healer to start heals just a split second sooner? They tell you to tank/dps better and not take as much damage. Those defenses are what cause issues like this to arise. I'm no saint myself, didn't even remember how to do some of the guildhest I get put into lately. Some low level explains it to me, that's something he/she deserves a commendation for, at the very least. People just need to relax and stop being so overly defensive about things, and be willing to try something new. How i learned to play SMN correctly, because I was botching it so bad, I couldn't get above healers emnity on simple fights, even with a relic on.

TL;DR version: Be a bit more open minded is all. You just might be surprised at what you can learn, from both new and old.