Best guide to programming you ever learn

[Lunasole]

That one is from Jet Propulsion Laboratory (NASA), originally about C language, but most of it applicable to Purebasic code as well.
It's of course the hardest way to code regular application-level soft following these rules (and is not necessary), but makes sense to listen up many of mentioned things.
Also this list is short and handy, unlike Knuth's book or something else.

http://lars-lab.jpl.nasa.gov/JPL_Coding_Standard_C.pdf

PS. In my code I'm constantly breaking about half of this standard, depending on mood and "current laziness level" :3