Suicide is a form of murder - premeditated murder. It isn't something you do the first time you think of doing it. It takes some getting used to. And you need the means, the opportunity, the motive. A successful suicide demands good organization and a cool head, both of which are usually incompatible with the suicidal state of mind.
It's important to cultivate detachment. One way to do this is to practice imagining yourself dead, or in the process of dying. If there's a window, you must imagine your body falling out the window. If there's a knife, you must imagine the knife piercing your skin. It there's a train coming, you must imagine your torso flattened under its wheels. There exercises are necessary to achieve the proper distance.
The motive is paramount. Without a strong motive, you're sunk.