A great web site for typographical tips. A couple of important items I still see violated frequently:
"You must always put exactly one space between sentences" -- putting two spaces after a period is a relic of the typewriter age.
"It would be awkward if the introductory heading ARGUMENT appeared on the last line of a page, and the actual argument started at the top of the following page."
We get papers at NYU with the second problem all the time -- the last thing on the page is the heading for what's on the next page.