Cowriting is very personal. A great song is an honest song, so you have to be able to open up to the person in the room. It's like a blind date. I know in the first five minutes if it's gonna be weird.
It's a job. Get up and do it every day. Show up. Don't say no. Taylor Swift was the third write of my day every week. If I had gone home or said “Ah, man. I'm tired today. I'm not going to write at 4 o'clock in the afternoon with a teenager.' If I had done that, just think. Keep an open mind. Everybody has something to come into the room with and when you're starting out, try everything. You might find your magical writing partner.