Step 1- Before splitting up into groups of two, write down 2-3 song title ideas, or a chord progression, or simply a lyrical melody. Anything to help get the creative juices flowing in your session. Coming prepared is always a good idea no matter how experienced you are at co-writing.
Step 2- After splitting into your group- define your songwriting goals for the day. Are you writing for a purpose or planning to just to go with the flow? Is this a personal song or something you expect to be commercially viable? Is it for one of you to sing or is the goal for it to be pitched to an artist?
Step 3- Bounce some of the previous written ideas off each other. If you aren’t sure about your lyrics or chord transitions, ask your collaborator for advice.
Step 4- Experiment with the ideas, even if they are bad ones. For example- try out several melodies or chord progressions until you find one you both love. Above all, ALWAYS respect what your co-writer has to offer. Even if you decide not to use certain suggestions, always show appreciation for their help. After all you would want the same treatment in return.
Step 5- Even if the song doesn’t get complete- Discuss what would happen if it had been completed. Is the ownership split 50/50? Will you demo it? who will pay for the recording? Who will register the copyright? Do you each want to be able to pitch it? Do you each want to be able to perform it? Etc...