It's late and I'm tired but I'll try and remember some things we do-
Explain to them that in the heat of the moment, they need to manage their reactions. They often need to use a strategy to calm down before it escalates. For eg. STOP and take 5 deep breaths, STOP and count to 10, STOP and leave the room for a minute. Then they need to use their words to tell the other person exactly what the problem is; what they want them to stop doing, why, and what they want them to do instead. For eg "Xyz can you please stop standing on my bed, it messes it up, can you use your ladder instead". (That bit is hard and doesn't happen much in our house, but I do manage to get them to do the calming bits at least). Remind them that yelling and hitting is not acceptable and they need to control themselves before it gets to that. They need to use their words only, and if they have no success with that, they can come and ask me for help.
I remind them to respect the other persons boundaries, personal space, and time to themselves. A common one for us is, x will ask y to play a game, y will say no he doesn't feel like it, so then x will badger y into playing, then y will play really stroppily, then x gets upset because y isn't into it. So I just remind them to always respect each others feelings.
I have explained to them about resentment, and how if x always annoys y, then next time x wants to play with y, y will say no because y automatically thinks that x will annoy him. Then we get this big cycle of anger.
When they DO play nice together, I give them lots of praise about what they're doing nicely, and comment about how nice it makes the whole household when everyone is happy.
That's all I can think of atm, but it is a big issue in my house, between my two boys. They just don't get along. :/