Not so much form related, but another important part of creating a good feud/storyline is getting to know the character you want to feud with. Anyone can send in a random attack, and set up a revenge match etc, but that's almost a lazy tactic when we're playing a game like this where everyone is offering so much information and content to be used.

Some of my favourite rping here, for example, was with Mark Flynn. We never needed to expressly have an out and out rivalry, because we knew how to use eachother's characters, and so whether it was tagging or facing eachother, we were never short of material. Knowing the other person's character allows you to add a level of depth to your feud that just isn't there any other way.

You can get to know your character's 'enemies' just as easily as you can get to know his/her allies, and draw just as much from that.