Here is how I do it:
1. Log into my server account.
2. Go the .htaccess file.
Note: If you do not know where is your .htaccess file, read this post.
3. Paste the custom code below onto the .htaccess file.
## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access 1 year"
ExpiresByType image/jpeg "access 1 year"
ExpiresByType image/gif "access 1 year"
ExpiresByType image/png "access 1 year"
ExpiresByType text/css "access 1 month"
ExpiresByType application/pdf "access 1 month"
ExpiresByType text/x-javascript "access 1 month"
ExpiresByType application/x-shockwave-flash "access 1 month"
ExpiresByType image/x-icon "access 1 year"
ExpiresDefault "access 2 days"
</IfModule>
## EXPIRES CACHING ##
4. Now click Save Changes.
*Another tip to increase your page speed by specify a vary: accept-encoding header.