Also be aware your own IP does not get stolen, or that people do not 'wiggle' themselves or manipulate you into owning part of your IP. I've had multiple attempts of people trying this. One outright stole my source code and rebranded and tried to market it, another, well, don't get me started.
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!
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.