robots.txt:
User-agent: *
Disallow: /specific_dir/
Disallow: /particular_file.html
in file:
<META NAME="robots" CONTENT="noindex">
more robots.txt info
additionally you can have nofollow command for a specific link, introduced by google
<a href="http://www.site.com/page.html" rel="nofollow">Visit My Page</a>