Based on the principle that כל המבקש רחמים על חבירו והוא צריך לאותו דבר הוא נענה תחילה - anyone who davens for someone and he himself needs the same thing, he is answered first - who is answered first if two people daven for each other?
The Daven For Me organization tries to match people like this. If anyone has participated in that program and knows, that would be a good answer. [Because I really like the song: the song/video that inspired the campaign.]