Here are a few other guidelines. These are mostly noted as a result of noticing issues in the existing documentation ...later, we can have a more coherent list.
\begin{verbatim} environment to format larger blocks of
source code.
\emph{ ... } environment for emphasis (italics), rather than
\em or \it.
\ldots macro to produce three dots (...) indicating
ellipses -- if you just write three periods in a row they are spaced too
closely (for example: ...).
\textbackslash or \verb|\| rather than
$\backslash$ (since in latex2html the first two options produce a
character, the third a GIF image).
.tex filenames. Use hyphens instead (i.e. use `-' instead of `_').
Normally, a good heuristic is to copy the existing examples in the manual when writing new ones. However, much of the LATEX here doesn't yet take advantage of these macros. So look at the description linked above instead for now.