Some of these I've read elsewhere, some I've created, all have been helpful in keeping me alive in tournaments. Please feel free to add some of your own!
*** Never go broke in an unraised pot. (Brunson, I believe.)
*** Never go broke with top pair.
*** If you have a pocket pair, so does someone else. (Probably not true, but it's a safe way to play.)
*** Just because 3 of a suit flopped doesn't mean you shouldn't bet your 2 pair or set.
*** Stop being afraid of "MUBs" (Monsters Under the Bed). The flop probably missed him too.
*** People often bet scare cards (third to a flush or straight, paired boards in unraised pots) and so should you.
*** Exploit c-bettors. However, you need to c-bet yourself.
*** You MUST vary your play. (I once played an entire SNG raising with any 2 where the second card dealt was a diamond. I lost, but it was a blast!)
*** Steal from LP, even in cash games. I've never understood why people are happy to raise with AKs from the CO and just win the blinds but turn their noses at winning the blinds with 74o.
*** Especially in tournaments, raise limpers. If it's worth playing, it's worth playing for a raise.
And, the number one truism of all time: AA is just a pair. You WILL lose with it sometimes. Get over it.
I know some will disagree with these, and probably rightfully so. These are just some of the things I keep in mind when playing and they work for me.