3. "Pay it off every month" In response to Reply # 0
That's the big thing. If you don't pay the balance every month then th interest starts piling up quick. I've got the Virgin America card which works for me but that's also because I fly Virgin often. You get 3x points for Virgin purchases so it works out for me. I also have some travel Amex card but I feel like I get substantially less points using that. The benefit of that one is no annual fee vs. maybe $50 for the virgin card.
5. "do the math to compare deals" In response to Reply # 0
i usually find that a specific "airline" or "gas" rewards card might actually give you less than a standard "cash back" rewards card if you convert the airline/gas rewards to a cash equivalent.
i used to have the bp rewards card from chase, and they would give 5% cash back for all purchases at bp.
that was definitely the best gas rewards offer at the time. i was getting probably $25/month back.
they changed the rules about a year ago, and now the reward is that you get a few cents per gallon off, instead of 5% cash back. it greatly reduced the amount of cash that i was saving with the card. i did the math and realized that it was about even with my 1% cash back card, so i usually just use that.
the card companies try to trick you by rewarding you with frequent flier miles, or speedway points, or in my case the cents off a gallon. i think they do that to it harder for you to understand what the rewards actually will be, or make it so that it seems like a lot, even when it really isn't.