Code as if the next guy to maintain your code is a homicidal maniac who knows where you live.
Make the right things easy and the wrong things hard to do.
Give users what they actually want, not what they say they want.
Just make people better at something they want to be better at.
Upgrade your user, not your product. Value is less about the stuff and more about the stuff the stuff enables. Don't build better cameras - build better photographers.
The best user experiences are enchanting. They help the user enter an alternate reality, whether it's the world of making music, writing, sharing photos, coding, or managing a project.