Don't partner up with someone who is just like you
Ideally, each partner brings something different to the table. One partner might have 15 years in the industry while the other partner might have a great deal of marketing talent. Overlapping strengths can become a point of contention between co-founders. They can also rob your business of the vital expertise that it needs to survive. Find someone who knows things you don't know and figure out how to partner with that person. Find someone who compliments your strengths.
Find someone who shares your visionYou believe in buying fair trade, your partner believes in buying cheap. You believe in serving only fresh, local food, your partner believes that it's better to import food. Your partner wants the latest and greatest technology; you're content to use 5 year old PCs. These sorts of conflicts aren't just about how things are done. These are conflicts that touch on the very heart of the brand and identity of the businesses they describe.
Craft a vision statement for your business, and make it meaningful in concrete terms. Find a partner who shares that vision. Then, whenever conflicts come up you can go back to the central question: "Does this course of action fit with our vision, or not?" Ideally, both of you should be excited about the direction your company is headed in.
Find someone you can communicate with
You need to find a co-founder who you can talk to-even when you don't agree. You can't afford to let conflicts and resentments fester. You also can't afford a scenario where both partners aren't aware of what's going on in the business. You both should feel comfortable expressing your opinions. You both need to feel like you're in an open, respectful relationship. Only then will your partnership-and the business you are building-flourish.