The following simple keyword rules that must be followed while writing.

• Always write for people first.
• Position keywords after the post are written.
• Keep the number of individual keywords limited.
• Avoid using a given keyword too frequently in a document. The Internet is not a first grade practice reader.
• Position keywords in titles, headers, in text, and on new pages.
• Position keywords in graphic descriptions as suitable to explain them. Remember some programs use those descriptions to construe images for readers who can’t see the graphics.
• Go back to read the text again read it as your human readers would. Take out the keywords that are unnecessary. Search engine spiders and people agree on that.

For more information http://www.johntp.com/2006/04/14/seven-simple-keyword-rules/