Don't underestimate the importance of picking your co-founders. This is the single most important decision you will make for your startup. Don't assume that just because your co-founder is your friend that he won't turn around and try to sue you later for code you sacrificed your time, health, and happiness for. If one of your co-founders is non-technical, make sure he/she has some semblance of understanding of what's possible/feasible to build with limited resources and data. Don't build in a bubble. Be collaborative with your team about the direction of your product. It's not always important that you make the right decisions, only that you ship something, test your assumptions, and pivot when needed. Don't for one second think that the "business" founder's input about the product is automatically more valid than your own. Arguing/discussion is healthy but make sure by the end of the day a decision is made the entire team is comfortable executing upon. Finally, if things are running fairly smoothly, make sure all legal documents are in order and everyone's interests are protected so aforementioned business founders don't sue you. </rant>