A single blank line is placed before and after it. Text within the comments is ignored by the browser. Comments can not be nested. If it is going to be a large site, consider subfolders. All graphics should be stored in an images folder and the site can be broken down by sections, with each folder corresponding to the section.
Navigation elements can be navbar.gif, navbuton.gif, etc.
A headline graphic may be hdbanner.gif. Another option is to make sure all files that belong on one page start with the same letter. Example wk1title.gif, wk1head.gif, wk1bkg.gif, wk1.htm. In general use lowercase letters. Never use a space in a file name.