Focus on your startup. Do not do anything else.
Paul Graham offers advice about how to keep your startup from dying:
The number one thing not to do is other things. If you find yourself saying a sentence that ends with “but we’re going to keep working on the startup,” you are in big trouble. Bob’s going to grad school, but we’re going to keep working on the startup. We’re moving back to Minnesota, but we’re going to keep working on the startup. We’re taking on some consulting projects, but we’re going to keep working on the startup. You may as well just translate these to “we’re giving up on the startup, but we’re not willing to admit that to ourselves,” because that’s what it means most of the time. A startup is so hard that working on it can’t be preceded by “but.”
In particular, don’t go to graduate school, and don’t start other projects. Distraction is fatal to startups. Going to (or back to) school is a huge predictor of death because in addition to the distraction it gives you something to say you’re doing. If you’re only doing a startup, then if the startup fails, you fail. If you’re in grad school and your startup fails, you can say later “Oh yeah, we had this startup on the side when I was in grad school, but it didn’t go anywhere.”
You can’t use euphemisms like “didn’t go anywhere” for something that’s your only occupation. People won’t let you.
One of the most interesting things we’ve discovered from working on Y Combinator is that founders are more motivated by the fear of looking bad than by the hope of getting millions of dollars. So if you want to get millions of dollars, put yourself in a position where failure will be public and humiliating.