First, I try to figure out what the tantrum is over so I can try and figure out where to go from there. Not that I can always figure that out, but it does help if I can see what he is upset about.
I usually pick him up and try to cuddle him explaining why he can't do x,y,z, in a gentle voice. Sometimes this works, sometimes it makes him even more mad. If it makes him even more mad, I put him back down. Sometimes this ends up being a pick up put down session because then he can't decide if he wants up and cuddled or down to scream when he's so upset.
Then I do my best to distract him and redirect him to something else.
That's basically what I do with my youngest. With my oldest, same thing, but he's old enough now to understand when I tell him there is no need to throw fits, and that he just needs to explain why he is upset to mommy. Obviously sometimes his emotions are too much, and the tantrum is a result. If I can't get him to calm down, I ask him to go sit on the couch until he can calm down or to go lay on his bed to calm down. Both work very well for him. He usually continues to cry for a few minutes, and then calms himself slowly. Once he has collected himself, he tells me he is calm and asks if he can get up now. I tell him yes, and then we talk about why he was upset and again, why he can't do x,y,z if the reason was me telling him no about something.
