The 10 commandments, of mapping...

[Woe Kitten]

Thou shalt place the player experience above all other considerations
Thou shalt love aesthetics, technology and player psychology utterly and equally
Thou shalt never cut corners
Thou shalt have others play your levels from the earliest possible stage and treasure their feedback
Thou shalt love and study the real world because, if though does't not know the real world, how does't though expect to make a convincing digital one?

Thou shalt play EVERYTHING to develop thy critical faculties
Thou shalt learn to communicate effectively with others and LISTEN
Thou shalt learn to think like a coder, an artist and a producer simultaneously
Thou shalt live with humility in thy heart and confidence in thy mind

Thou shalt sleep (occasionally)

[stoopdapoop]

I was with you up until that last one.

[MayheM]

Thou shalt never use other mappers custom content without asking first, but most importantly thou must give credit.
Thou shalt use criticism as a learning tool, for it is one of the greatest you will know.

[joe_rogers_11155]

hark, thou shalt boycott all valve products until a suitable replacement for Hammer is released

[MayheM]

I am suddenly reminded of the great Mel Brooks...

[ReservoirWOLF]

THOU SHALT LAUGH AT MEL BROOKS

[Dr Evil]

lawl...

[Dr Evil]

[surgeon]

Always use fog, even if it's an all-indoor map, or a sunny outdoor map.

Even if you set the end distance to 15,000, it reduces contrast in the distance and helps separate the foreground from the background. So many times I see custom maps or people's first maps and they have no fog_controller, it just looks plain bad however nice the map is.

[Guessmyname]

Thou shalt always colour your lights. No light should ever be left at default values.

[Ashfall_2008]

Thou shalt design your areas with gameplay in mind first not asthetics. Once gameplay is perfect only then shalt though change textures and add models to make it look pretty...