Search Engines read a yourserver.com/robots.txt file to get information on what they should and shouldn’t be looking for, and where.
Specifying where search engines should look for content in high-quality directories or files you can increase the ranking of your site, and is recommended by Google and all the search engines.
An example WordPress robots.txt file:
Sitemap: http://www.example.com/sitemap.xml
# Google Image
User-agent: Googlebot-Image
Disallow:
Allow: /*
# Google AdSense
User-agent: Mediapartners-Google*
Disallow:
# digg mirror
User-agent: duggmirror
Disallow: /
# global
User-agent: *
Disallow: /cgi-bin/
Disallow: /wp-admin/
Disallow: /wp-includes/
Disallow: /wp-content/plugins/
Disallow: /wp-content/cache/
Disallow: /wp-content/themes/
Disallow: /trackback/
Disallow: /feed/
Disallow: /comments/
Disallow: /category/*/*
Disallow: */trackback/
Disallow: */feed/
Disallow: */comments/
Disallow: /*?
Allow: /wp-content/uploads/