Don't neglect this one. A surprisingly large number of small companies that go under are profitable. They don't go under because they're making a loss; they go under because they cannot pay today's bill. Cash flow kills small businesses dead.
you must enjoy the job, because at some point your work under the pressure of a customer.
be very wary of intellectual property issues (IP issues are not very well understood and some people will think you steal their IP when you're not; and being stolen will make them very angry, like lawsuit-angry)
be ready to work according to someone else's planning : during your weekend, when you need to sleep, when you're sick, etc.
be ready to contemplate the fact that there are some people who take much and gives quite less.
There are a lot of bastards out there. Hindsight is 20/20, but there were multiple cases where things didn't feel right, I ignored that and went ahead anyway, and everything went sideways.
Always trust your spider-sense!
- don't run out of cash
- make something you enjoy working on
- sell something people need
- sell something for more than it costs to make
- don't expect the people around you to be as excited as you are about your thing