People get treated so much at the end of life when there is little to be gained. It's not really ethical.
When you're old and sick, you might become tired of the medical care process. In this situation, dying can be pretty straightforward. The hard part is beforehand, sorting through medical options and deciding if any are worth it. Let's assume - a big assumption - that you've done that, and you have decided that it's time to die. I also assume you're not going to kill yourself, because that's illegal, and many people think it's immoral. America isn't ready for that yet.
Please don't think me callous for making this into a checklist.
1. Talk to your family and friends. They may want to talk you out of it, but you don't have to listen. If you don't talk to the people around you, they may try to stop you from dying, by allowing medical treatment once you become unconscious or confused. Or they may start arguing with you in the doctor's office, which can delay things. Instruct your family and friends that once you become unconscious, not only do you not want any resuscitation, you want pain medications delivered to you every time you appear even a little bit uncomfortable.
2. Tell your doctor. The magic words are "do not resuscitate," "do not intubate" and "comfort care."
3. Complain to your doctor about anything unpleasant that happens. Short of breath? Call for some morphine. Anxious? Call for some Ativan. Pain? There are a hundred options.
4. Don't eat or drink if you don't want to
5. Don't accept medical treatment for anything, including things like pneumonia or bleeding. Instead ask for symptomatic relief.
6. Get a hospice program, or a palliative medicine specialist, involved if you can.
7. Go to sleep.
Along the way, you should probably get all your affairs in order, etc., but I'm a doctor, not a lawyer, and I'll leave that to those other professionals.