google optimize

http://www.google.com/support/webmasters/bin/answer.py?answer=35769

1 meta description
meta name="Description" content="Author: A.N. Author, Illustrator: P. Picture, Category: Books, Price: £9.24, Length: 784 pages"
2 title
3 site map
4 title tag and ALT
5 If-Modified-Since HTTP header
a) If the request would normally result in anything other than a
200 (OK) status, or if the passed If-Modified-Since date is
invalid, the response is exactly the same as for a normal GET.
A date which is later than the server's current time is
invalid.
b) If the variant has been modified since the If-Modified-Since
date, the response is exactly the same as for a normal GET.
c) If the variant has not been modified since a valid If-
Modified-Since date, the server SHOULD return a 304 (Not
Modified) response.