Вы можете использовать эти правила:
ErrorDocument 404 /404.php
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^ http://www.%{HTTP_HOST}${REQUEST_URI} [L,R=301,NE]
RewriteCond %{THE_REQUEST} /index\.php [NC]
RewriteRule ^(.*)index\.php$ /$1 [R=301,L,NE]
# Unless directory, remove trailing slash
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.+)/$ /$1 [NE,R=302,L]
# remove content after 2nd slash
RewriteRule ^(.+\.php)/.*$ /$1 [L,NC,R=301]