[note: this is for the noobs, not the l33t]
[note to self: find the damn usb-cable]
Hello there, my name is Viktor and today I will explain to you in detail how to clean your computer from dust.
You will need:
First, unplug your computer. Then remove the side door. Unplug all the hardware, if you know that you are going to ask yourself "cable goes where?" after you are done cleaning, draw yourself a map or something. I'm serious.
Unscrew and unplug all the hardware. Do not put it near some sort of liquid. If you have a anti-static bag or something, put your hardware on that.
Clean all the hardware with canned air. Be extra careful when cleaning the RAM. Do not put your fingers all over it.
Remove the cpu-fan. Note that you should only remove the fan if you do not wish to put on some new thermal paste. Clean it with canned air.
If you havent removed your PSU already, do it now. Clean all the holes with canned air.
Use the rest of your canned air to clean you case and fans.
I think that would cover it all...for now. If you have any questions, feel free to ask.