Lilly and Patrick both throw killer tantrums sometimes, but I realized that when I say that, it's not always clear what I mean. My strategy (which I didn't even notice until recently) is to highlight smaller episodes of bad manners; calling those "tantrums," or reproving the kids for acting out, before they end up screaming and losing it, seems to keep a better hold on the day.
Let me explain. Or at least sum up. (Princess Bride, ten points.) The other day at lunch, Patrick did something he commonly does: he quits eating, and when I ask him to take a bite, he grunts at me. Sometimes he'll pick up food and put it between his lips, staring at me and letting it sit there. Regardless, he very definitely is no longer eating. This, to me, is a tantrum. This is unacceptable behavior.
When he does something like this, I ask him if he's going to eat, or if he would prefer to throw a tantrum. Cue more grunting. If he continues to not eat, I tell him that there are no tantrums allowed at the table, and he must go up to his room if he doesn't want to eat. He rarely leaves the table voluntarily, so usually I carry him upstairs.
Am I too strict? Sometimes I think so. But, I really do think that this cuts back on the number of blowout tantrums. They know I don't tolerate misbehavior. And, to be honest, I expect a lot from them. They are almost three and a half. Still very much young children, but also plenty old enough to cooperate. I know my expectations are high, but it's not harming them, and it makes the rest of our lives so much nicer.