1) sprawdź czy twój hosting ma zainstalowany mod_expires - moduł Apacha
2) w pliku .htaccess
dodaj :
Kod:
<IfModule mod_expires.c>
ExpiresActive On
ExpiresDefault "access plus 1 seconds"
ExpiresByType text/html "access plus 2 seconds"
ExpiresByType image/gif "access plus 6 weeks"
ExpiresByType image/jpeg "access plus 1 weeks"
ExpiresByType image/png "access plus 6 weeks"
ExpiresByType text/css "access plus 90 minutes"
ExpiresByType text/javascript "access plus 6 weeks"
ExpiresByType application/x-javascript "access plus 6 weeks"
ExpiresByType text/xml "access plus 1 seconds"
ExpiresByType application/x-shockwave-flash "access plus 6 weeks"
</IfModule>
przykładowe wartości