In startups, it's all about the team. Ideas change, business models change and even roles can change, but the hope is that you can build a core team that is lasting. From the first step of finding a good co-founder to adding key members to your early team, it's a good idea to have a framework for what you're looking for. What I look for are the 3 C's: Chemistry, Competence and Customer Focus.
You can't throw a stone in the startup community without hitting a blog post, tweet, or discussion around co-founders. While I think there's a great deal of good advice out there on the search for a co-founder on places like Venture Hacks, Humbled MBA and OnStartups, it's as important to understand the potholes to avoid. Just like a pothole will disable an otherwise great car, these mistakes will derail your company...and your cofounder search.