In the beginning we drew up diagrams for database tables, wrote out what made us different from competitors, why people would like us, wrote a version of the site, then scrapped all of it and rewrote everything multiple times over in several months. At this point it was just us doing this in our spare time.
As time went by, I realized my cofounder wasn't going to give up as much as I was willing to, and that's when I realized I need a backup plan or two. My cf is a great hacker and decent at design, so one plan was to go solo, but my design sucked. Another plan was a different site where design didn't matter, so I decided to work on this second site while waiting for my cf to switch from a second job freelancing to rejoining the project. Lesson here is simply have backup plans.
Finally his girlfriend broke up with him and we are bros again. He put down the framework for our new attack plan and I started hacking away on the meat of it. He refused to keep working until we talked with clients, so I set up some meetings. Now I'm hacking half the time, doing the business side the other half, and maybe a couple hours for eating and spending time on HN and so on. After meeting with clients to find out what they want, I was sure he would be into it. Wrong. Now I have to handle clients which means a lot of socializing and a lot less hacking, yet I have to code the four or five features that the clients requested.
You may think get another founder, but you guessed it, I tried. I know several people who would make great founders. The problem is that they can't give up their social lives and that's really what you have to do until you can hire people to take some of the weight off your shoulders. Specifically, girls are a major interest to them. And as most of us know, having a girlfriend (or wife in one case) is a full time job.
So be prepared to multitask and try to account for losing your founder (I never thought it would happen: I've known mine since 1st grade). Also have a backup plan and maybe learn what you are weak at (design in my case) to a reasonable competency.