10 .htaccess code snippets you must have in hand.

.htaccess

# Accompanies this blog post:
# http://www.seomoz.org/blog/htaccess-file-snippets-for-seos

# NOTE: This file isn't designed to be used all together, some of the rules will conflict,
# it is meant more as a copy and paste board.

# IMPORTANT: Make sure you test .htaccess changes thoroughly, as it can be easy to make mistakes
# and then you end up in a bad place!

RewriteEngine On

#
# 1) Make URLs SEO Friendly and Future Proof
#

<Files magic>
	ForceType application/x-httpd-php5
</Files>


#
# 2) Apply rel="canonical" to PDFs
#

<Files download.pdf>
	Header add Link '<http://www.tomanthony.co.uk/httest/pdf-download.html>; rel="canonical"'
</Files>

<Files product.jpg>
	Header add Link '<http://www.tomanthony.co.uk/httest/product-page.html>; rel="canonical"'
</Files>

RewriteRule ([^/]+)\.pdf$ - [E=FILENAME:$1]
<FilesMatch "\.pdf$">
	Header add Link '<http://www.tomanthony.co.uk/httest/%{FILENAME}e.html>; rel="canonical"'
</FilesMatch>


#
# 3) Robots Directives
#

Header set X-Robots-Tag "noindex, noarchive, nosnippet"


#
# 4) Various Types of Redirect
#

# Ensure www on all URLs.
RewriteCond %{HTTP_HOST} ^example.com [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301]

# Ensure we are using HTTPS version of the site.
RewriteCond %{HTTPS} !on
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

# Ensure all URLs have a trailing slash.
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !(.*)/$
RewriteRule ^(.*)$ http://www.example.com/$1/ [L,R=301]


#
# 5) Custom 404 Error Page
#

ErrorDocument 404 /cool404.html

# Can also do the same for other errors...
ErrorDocument 500 /cool500.html


#
# 6) Send the Vary Header to Help Crawl Mobile Content
#

Header append Vary: User-Agent


#
# 7) Improve Caching for Better Site Speed
#

<FilesMatch ".(flv|gif|jpg|jpeg|png|ico|swf|js|css|pdf)$">
	Header set Cache-Control "max-age=28800"
</FilesMatch>


#
# 8) An Apple-style 'Back Soon' Maintenance Page
#

RewriteCond %{REMOTE_ADDR}  !your_ip_address
RewriteCond %{REMOTE_ADDR}  !127.0.0.1
RewriteRule !offline.php$ http://www.example.com/back_soon.html [L,R=307]


#
# 9) Smarten up Your URLs Even When Your CMS Says No!
#

# Rewrite a specific product...
RewriteRule ray-guns/ product.php?id=3123

# ... or groups of them
RewriteRule product/([0-9]+)/ product.php?id=$1


#
# 10)  Recruit via Your HTTP Headers
#

Header set Hiring-Now "Looking for a job? Email us!"