Stand at the top of a tall structure and make sure that there is something relatively soft such as grass, or a sleeping fat person, below. You should preferably be on the edge of some kind of overhang, such as a bridge.
Next, tie cheese wire around your neck - tight enough that it won't slip off under tension but loose enough not to choke you. Remember, you don't want to die looking like a Michael Hutchence wannabe. Nobody wants to be Michael Hutchence. Even Hutchence hated it.
Anyway, tie the cheese wire to something solid on top of the structure. Make sure that there is a good six or seven feet of slack. To traumatize any police, medical personnel or curious children who may investigate your corpse, write "I DID IT FOR THE LULZ
!" across your chest. Now stand at the edge and glue your hands to the side of your head. If you are under the age of 16, you may wish to get a responsible but sociopathic adult to help you. Wait until your hands are glued solidly to your head. This has the added advantage of stopping you from calling for help if you change your mind.
Now jump off the structure. It'll only hurt for a second, when the cheese wire runs out of slack and slices through your neck. The overhang should stop you from bashing your now-severed head against the wall of the structure when the cutting motion jerks your body backwards.
You should hopefully land face down, although this is really out of your hands by now. Unlike your head, which is glued to them. This has the excellent effect of causing whoever finds your body to think that you have pulled your head off.