Here's what I do:
Once you know a SAM has been launched, turn towards it, padlock it, and then turn away and keep it on your 3-9 o'clock axis. Drop chaff. Don't overdo the chaff, you have a limited supply. Turn on your ecm jammer ASAP. There's no reason that I know of to save it.
As the missile approaches, you might begin a tight turn, and drop some chaff. It can't match your turn, unless you begin your turn too early. Also, you might want to get real low, almost to ground level, where tracking you is more difficult. Again, drop some chaff, but be careful about turning into your own chaff with the missile chasing it.
I have found that this works pretty well. If the missile is behind you or to your front, you will get hit.
HARMs are great, but use them on the deadlier sites sites first. They are not a substitute for evasive maneuvers.
I don't play OIF that much, so I hope these instructions help until someone with more experience posts a reply.