1. It's all about fulfilling certain gear requirements. At least to be able to enter the 'real' endgame consisting of heroics and raiding.
2. Without the proper gear, you are undergeared and will not be able to perform in a group. This should go without saying, but obviously it doesn't. Note: I haven't been shrewd enough to hide this fact that I'm lacking...
3. People do not read the notes you write into the LFG tool. Really.
4. People do not care if you have put yourself into the queue for a NORMAL instance: the assumption is that if you are level capped, you are prepared to take on anything and beyond. That includes Algalon.
5. If you are a newcomer -and state that clearly to the group- be prepared to get two kinds of responses. First one is outright calling you "noob", which should be false. The other one is the professional -guild like- response "Ok, this is how we do it..."
6. If you're tanking, after the first wipe there are two responses, too. First one is "Noob tank!" continued with "DK tank next". The professional -guild like- response is "So we failed, I had this problem and we should try it like this next..."
7. PUG's teach you only one thing: to be selfish and need everything that drops.
8. Usually in any MMO, politeness goes a long way. "Sorry" and "Thank you" are powerful things to say.
9. In most PUGs, the former doesn't apply.
10 You shouldn't look into the gift horse's mouth: that is, when the PUG starts and there are two or more hyperactive kids fooling around, it doesn't mean that the instance is failed.
11. Expect the unexpected. Like the former hyperactive PUG performing top notch, or the stiff upperlip group failing miserably.
12. Blow your cooldowns early rather than late.
These lessons I have learned from 'only' less than ten ToC normal PUG runs in WoW. The best runs have been the ones with the guild, granted that the runs were meant to gear up us newly dinged 80's and there were a couple of very capable players with accordingly capable toons. The worst have been the runs with two players, who claim they know how to play and what to do, but do not see their shortcomings. These are the source of the name calling and noobishness themself.
Sad to say, it's the first time I've put anyone on ignore list for the conduct they have presented in a PUG instance run. Then again, any MMO would be much newcomer friendly without these arrogant kids, who do not see that the instances can be run more effectively by playing in co-operation rather than soloing.
More lessons to learn, and most certainly more things to report from the casual side of the hardcore mind.