One of the way to Set cache expiration is by using .htaccess file.
Below code will set expiration for it's respective file type, e.g. for CSS files expiration will be 14 days.
<IfModule mod_expires.c>
ExpiresActive on
ExpiresDefault "access plus 1 month"
ExpiresByType application/javascript "access plus 1 year"
ExpiresByType image/x-ico "access plus 1 year"
ExpiresByType image/jpg "access plus 14 days"
ExpiresByType image/jpeg "access plus 14 days"
ExpiresByType image/gif "access plus 14 days"
ExpiresByType image/png "access plus 14 days"
ExpiresByType text/css "access plus 14 days"
</IfModule>
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