[Details] Make sure that each page of your site is accessible with a stable address (URL) and that the HTTP caching properties are set correctly. Make sure if you migrate to a new site version that the URLs are either kept as is or at least redirected to the new ones. [Rationale] HTTP is a very powerful protocol and you get most of its power with stable URLs and an efficient caching system: bookmarks and links don't break, network access is faster, users are happy! [Test tool] The W3C Link Checker can provide some help. Besides, the advices given in the Common HTTP Implementation Problems Note can help assess what needs to be respected. [Requirement] 
Use HTTP properly