This one is perhaps the most obvious if any are available to you. There are a variety of firearms to choose from, ranging from your average Colt to maybe that sawn-off you have stashed away for a rainy day. Whatever you choose to go with, it is important to pull the trigger at the correct point. A shotgun blast to head will definitely end it while a bullet to the stomach may leave you slowly bleeding on the ground. We'll assume you want the first so pull it in a vital area, again, preferably the head.
You may want turn the lights off when you do - in the dark. The bullet will penetrate your skull and you will be gone from this earthly world. Of course this method is very messy. Just keep that in mind if you live with people. Overall this is a classic way to kill yourself.
Effectiveness: 9
Note that this is for fun and not to be taken seriously.