I've cleaned out obsolete information, and rearranged it so basic stuff tends to come first, and included the bugs and tips mentioned in this thread. I moved the old version to the bottom of the Tips/How-To list temporarily, in case I've overlooked something from there that I should put in the new version.
New version: https://www.physicsforums.com/help/latexhelp/
Old version: https://www.physicsforums.com/help/latexhelp-old/ [Broken]
Please feel free to post corrections etc. here!
Suggestion to add:For some reason, the following functions are not supported: arcsec arccsc arccot sech csch arcsinh arccosh arctanh arcsech arccsch arccoth