Hi,
You have to make some change sin your .htaccess file
You can check following tutorial for details.
http://gtmetrix.com/leverage-browser-caching.html

thank you

Check out http://css-tricks.com/snippets/htaccess/set-expires/

Hey Ray and Mamal,

Thanks for your replies. But I'm sorry I forgot to mention that I've already had browser caching added to my .htaccess file since day 1. However, somehow it doesn't work with DO's server. I do not know what other settings must I change. Below are the browser caching I've written to my .htaccess file:

## EXPIRES CACHING ##

AddType 'text/html; charset=UTF-8' html
# Add correct content-type for fonts
AddType application/vnd.ms-fontobject .eot
AddType font/ttf .ttf
AddType font/otf .otf
AddType font/x-woff .woff
AddType image/svg+xml .svg
ExpiresActive On
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/pdf "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/javascript "access plus 1 month"
ExpiresByType application/x-javascript "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresByType font/ttf "access plus 1 year"
ExpiresByType font/otf "access plus 1 year"
ExpiresByType font/x-woff "access plus 1 year"
ExpiresDefault "access plus 2 days"

## EXPIRES CACHING ##

Looks like the lines "" after ## EXPIRES CACHING ## and "" before ## EXPIRES CACHING ## got eaten up above.

Ah, the lines still got eaten up! I hope you guys know what I'm talking about. Let me give it a last shot. Here you go:
''
''

Looks like there's no way to put the lesser and greater than signs without them being eaten up. Anyway, here are the 2nd line (after the ## EXPIRES CACHING ## ):

IfModule mod_expires.c

and here's the 2nd last line (before ## EXPIRES CACHING ##):

/IfModule

Both lines are closed with the lesser and greater than signs.

Hey,

I managed to solve the problem. What I did was I enabled 'expires' in Apache.

Thanks, guys! :)