wondershaper is an easy to use traffic shaping script that provides these improvements:

* Low latency for interactive traffic (and pings) at all times
* Allow websurfing at reasonable speeds while uploading / downloading
* Make sure uploads don't hurt downloads
* Make sure downloads don't hurt uploads

official webpage :
http://lartc.org/wondershaper

about the ubuntu package :
http://packages.ubuntu.com/hoary/net/wondershaper

/usr/share/doc/wondershaper contains readme files. You might want to read these also.

I'm using firestarter together with wondershaper. Nothing has to be changed to firestarter.

So here we go :
sudo apt-get install wondershaper

use ifconfig to determine which of your networkcards is the one that is connected to your modem (and thus the internet).

$ifconfig

the networkcard that has your normal ip adress is the one (not 192.168.x.x)

Go to a speedtesting website (for example a speedtesting website by your internet provider or www.speedtest.nl if you live in the netherlands) and determine your average upload and download speed. Use these speeds as a guide.

$sudo wondershaper eth1 downspeed upspeed

download a big and uncompressable file while pinging to a fast and stable server on the internet or to your modem and adjust your downspeed until you are satisfied :

$sudo wondershaper eth1 downspeed upspeed

Now do the same with uploading a big and uncompressable file.

You have to tweak these settings a while until you are satisfied. When you are ready you can make these connection settings permanent by :

$ sudo pico /etc/network/interfaces

add these lines under eth1 if eth1 is your internetconnection. Change eth1,upspeed and downspeed to your settings.

up /sbin/wondershaper eth1 downspeed upspeed
down /sbin/wondershaper clear eth1

And we are done!

Source: Ubuntuforums.org