The Realities of Co-Writing
Figure out where you're going
You are going to co-write with someone you have never worked with before, so do your homework.
Ask them to give you a CD or link to two or three of their songs that they are excited about. This applies even to a hit writer, because past hits may not necessarily reflect his or her current attitude toward writing.
If the co-writer is an artist, get a copy of his or her latest recorded work. Ask them if they loved or hated it, because either way, you will have a sense of direction when you sit down to write with them.
Now, most important of all, bring at least two covered dishes to the picnic: if they don't like your potato salad, they may love your fried chicken. In other words, your co-writer may not be into a big ballad that day, but may really get off on a song at 120 beats per minute. If you both bring a couple of ideas to the session, odds are that out of the four ideas, one will appeal to both of you.
Don't force it
If none of the ideas work out, go have lunch or dinner. Talk about the weather or golf or knitting or fishing (not religion or politics) and then book another time a few days down the road to try to write again. If you repeat the process, and it still doesn't work, you may be better off as good friends than frustrated co-writers.