You may need to convert URI levels to query string parameters, for example if want to be RESTful compliant with PHP.
Try this one:
RewriteEngine on RewriteRule ^/(\w+)/(\w+)$ /path_of_index.php?lev1=$1&lev2=$2 [QSA,L]
In this case the first URI level will be converted to a query string parameter called lev1, while the second will be converted to a query string parameter called lev2, each one with the respective values.
For example, the uri /user/list will be passed to index.php and will become index.php?lev1=user&lev2=list
An eventual query string will be passed, eventually overriding lev1 and lev2 parameters.