Honestly, networking. You'll need to vet a lot of people, which means you'll have to talk to at least 10x as many before you find a good match that your comfortable with.
I've also used services like CoFounders Lab, and several others which have been suggested. They're all pretty mediocre at best.
I've also used services like CoFounders Lab, and several others which have been suggested. They're all pretty mediocre at best.