I just installed a SEF component on one of my sites. I’ve downloaded sh404SEF from Joomla Extensions Site and installed to seoimproved.com. I couldn’t succeed installing it from the first time, so i had to investigate a few minutes on web.

Here are the steps to follow:

1. Install the sh404SEF as a module extension from the administrator area.

2. Activate the Search Engine Friendly URLs from the Site > Global Configuration menu item:

3. Activate the Plugin from the Administration area.

4. Goto sh404SEF Configuration (Components > sh404SEF) and set “Rewriting mode” to “with .htaccess(mod_rewrite)”:

5. Rename the htaccess.txt to .htaccess and uncomment the RewriteBase line and the third section and comment the default Joomla Core SEF Section:

# Uncomment following line if your webserver’s URL
# is not directly related to physical file paths.
# Update Your Joomla!/MamboDirectory (just / for root)

RewriteBase /

########## Begin - Joomla! core SEF Section
############# Use this section if using ONLY Joomla! core SEF
## ALL (RewriteCond) lines in this section are only required if you actually
## have directories named ‘content’ or ‘component’ on your server
## If you do not have directories with these names, comment them out.
#
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional - see notes##
#RewriteCond %{REQUEST_URI} (/|\.htm|\.php|\.html|/[^.]*)$ [NC]
#RewriteRule ^(content/|component/) index.php
#
########## End - Joomla! core SEF Section

########## Begin - 3rd Party SEF Section
############# Use this section if you are using a 3rd party (Non Joomla! core) SEF extension - e.g. OpenSEF, 404_SEF, 404SEFx, SEF Advance, etc
#
RewriteCond %{REQUEST_URI} ^(/component/option,com) [NC,OR] ##optional - see notes##
RewriteCond %{REQUEST_URI} (/|\.htm|\.php|\.html|/[^.]*)$ [NC]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule (.*) index.php
#
########## End - 3rd Party SEF Section

Download from here a .htaccess file which is already configured to support sh404SEF.

See also: http://www.dart-creations.com/…/sef-for-joomla.html