<IfModule mod_rewrite.c>
Options +FollowSymLinks
RewriteEngine On
 
RewriteCond %{REQUEST_URI} /search.php$
RewriteCond %{QUERY_STRING} ^q=([A-Za-z0-9\+]+)&s=Search$
RewriteRule ^(.*)$ /s-%1? [R=301,L]
 
RewriteRule ^s-(.*)$ /search.php?q=$1&s=Search&a=1 [L]
</IfModule>

http://www.talkincode.com/using-mod_rewrite-on-form-parameters-89.html

Great way to use mod_rewrite with friendly URLs and Form

Using mod_rewrite On Form Parameters

url, php

Apache