I think a lot if the time with toddlers it depends what the tantrum is over. I know people who disagree and do things differently, but a lot if the time at that she it's just that their emotions are so overwhelming that they don't know how to handle them. If I can see a tantrum coming I try distraction, I still do it now if I can see one getting wound up with the other and they are starting to bicker. I'll go "quick what's that over there?!" Sounds funny I know but even making out I saw a spider can be enough to break the mood. Time ins instead of time outs. Taking them somewhere they can calm down, safely, with you there rather than say a 'naughty spot'. If it's something they want but can't have (today my 4 year old wanted to go in the garden after his bath and he isn't well so he cried about it when I said no) I told him I knew he wanted to and was sorry that he couldn't be it was late and offered him a cuddle. Or depending on the situation I just say "fine I'm going to do this/be in this room, come find me when your done crying"
That's just me though and I don't think there is a wrong or right way to do it, it's finding what with a for you. As long as you are consistent and firm, it will eventually get there, and tantrums will be less often.