To avoid duplicate content I use the
<NoIndex> </NoIndex> tags around the parts of my HTML I don't want Google to see.
Here are some useful HTTP headers
Code:
Cache-Control: spider-cache, must-include
Accept: image/jpeg, application/x-ms-application, image/gif, google/serp, bing/res, yandex/pravda, baidu/info
Content-type: text/plain
Content-Disposition: inline; phrase="free porn"