In my experience, the #1 rule is to BE NICE TO THE STAFF. This is especially true when something goes wrong. When something does go wrong, find out who actually has the authority to do something about it and deal with them. There is no point wasting effort with someone who has no ability to help.

Two examples:

1) I was standing by for an earlier flight.... they said they'd try to get me on - the flight was fairly full, but "maybe" a seat in the middle somewhere. Someone else came up ranting... literally pushed his way on in front of me. The GA threw her hands up and made a sort-of apology. I said, "I don't know how you put up with this all day." I was rewarded with a FC seat on a flight about 1 hour later (still 4 hours earlier then my original flight).

2) Travelling with my family - including two (then small) children. Flight was oversold, and an earlier equpment change had rearranged our seat assignments. I asked politely when we checked in whether they could at least have us 2 and 2 - didn't think we could board if the kids were not each with a parent. The GA took my boarding passes & said she'd see what she could do. A few minutes later, another passenger came along with the same complaint - but he had 4 tickets in first class. He screamed at the GA for the better part of 45 min. He got his seats together - in coach. I got (his, I suppose) in First.