Don't pyramid purposely.
Say you do 2 sets for bench [this seems to be everyone's favourite exercise!]
After a nice progressive warm up with medium to low reps [I really hope you know what a progressive ewarm up is - if not, this board needs help!]
Ok, you have a nice bag of blood in your pecs.
Go straight into your heaviest set and get as many reps as you can - in other words, go to failure.
Second set, again get as many reps out as possible, maybe even increase the weight if you think you can handle it.
I say don't pyramid purposely cause you may find on some days you can do more reps on your second set!