Complexity scales exponentially with the number of added features.
Optimize the right thing(s).
UX
You are not the typical user.
The easier you make it for someone to do something, the more likely they are to do it.
Users don’t read.
If in doubt, do the default.
If in doubt, make a mistake.
Users develop models, except they don't. They develop habits.
No one will solve a problem when they know a workaround.
For clients
What, not how.
Observed trends
Not actually maxims, but rather some trends that can get you into trouble.
Design
Make corner cases no more difficult than typical cases, even if it makes the typical cases cumbersome. (See “Universality begets complexity,” and “Optimize the right thing(s)”.)
UX
Minimum plausible affordances.
Mithat's Laws of Opinion
For every opinion, there is an equal and opposite opinion.
An opinion in motion will remain unchanged even when acted on by an external force.
The acceleration of an opinion depends on the outrageousness of the opinion times the number of times the opinion is seen.