how do you test the thing you intend to hang yourself from? how long does it take to pass out? how painful is it on a scale of 1 to 10? how long does it take to die? will you be brain damaged if you fail, and how severe will the damage be? what will your corpse look like? anything else i need to know?
Tie the rope to your chosen spot, and try putting your whole weight into it, and see if it holds. That's important.
It shouldn't take long to pass out, something like 15-30 seconds. I haven't been able to achieve this yet, so I'm not positive. It shouldn't be painful at all. If you feel pain, you're doing it wrong (I'm still failing this part as well).
Brain damage is a possibility if you're rescued a few minutes after losing consciousness. That's why you should do this in a secluded spot, hotel room, or at home only if you have at least an hour alone, without interruption.
Hanged corpses can be quite gruesome, but no much. It's easy to find pictures online. They do make me queasy, though...