we ask our 2.5 yr old to go to his room, get his sooky and dummy and when he's calmed down tell him to call out or come out and have a cuddle/drink/something to eat. But he's not to come back out til he's calmed down. Dummy and sooky seem to cure most tantrums (although we hate him having a dummy, but that's a whole new thread lol).
if he's really hysterical, we put him in his room.
If he starts to get aggressive ie hitting me/sister or throwing things his door gets shut (missiles removed). once he's stopped hitting/throwing stuffs but is still crying/melting down, I ask him if he'd like a cuddle. he usually says "yes peese" so we have a cuddle and a chat and kiss and blow nose, wipe face, sometimes a book. a little affectionate chat.
I have also found, that just as a tantie starts, if i get down to his level and say "*name* I know you are feeling upset/cranky/mad/frustrated that you can't do what you want/have that toy/whatever but the reason i said no was because ...... Perhaps you can play/eat/have this more suitable thing/object/task/show etc".
I also do try and stay calm although that is more successful some days over others! but just 'deal it with".
"okay i can see you are very upset about that, how about you go to your room, get your sooky and dummy and have a bit of quiet time on your bed while you calm down. When you are calm you can come out and have a cuddle." then go on with what i'm doing to show him that him carrying on like a pork chop isn't going to affect me or home life.

it can be very difficult.