Love, love and more love! Empathy and consistency are key, as is letting my child know that I listen to him and try to understand why he is behaving in a particular way. We also try to find solutions to challenging behaviour together, so that he is involved and feels validated. Also, I see myself as a role model so when I am upset, angry or frustrated, I don't hide these emotions from him but tell him how I am feeling and also discuss how I cope with them without hurting or upsetting other people. And I am very careful to apologise after doing anything that might have caused hurt!
After the situation I've found it useful to talk about what has happened so that I can understand the trigger and we can discuss acceptable future behavior. Time out works for a tantrum as sometimes it just gives my some time to chill out and to calm himself. I see this as less of a punishment and just what he personally needs to calm himself down.
I've found that yelling doesn't accomplish very much, so talking and helping them to understand the situation more. When I have yelled, all I have done is set the bar for the volume of the tantrum, and this doesn't help. Instead, I try to find a way to help my child calm down and then talk it through.