Following might be disturbing, but it is my experience and my thoughts. So you are warned!
So... I have tried to kill myself. I was almost successful with that. I hanged myself. But there was still some very little tiny desire to live and I didn't make knot to the doorknob too tight. Giving me a chance. I was lucky to live. Only before I saw and felt death very close. Death wasn't frightening. Very emotionless. Black fog rose from the ground and lifted me into weightlessness. I was floating there, inside the thickening fog. Light was fading and voices from the street got more and more distant I started to fall into complete darkness via vertical tunnel. And then there was nothing.
First I felt my existence again. I didn't know where I was nor why. I knew I existed. Then suddenly I started to hear sounds from the street like someone has turned volume on. Then I started to feel my body and limbs that were crisscrossed in an uncomfortable position. Only then I remembered what has happened. I just had escaped dark void.
I felt guilt that I had done that. What my parents would have felt finding me hanging there on the door!!! And my little brother? Especially him.
When I feel bad again, I think of him, that he needs me. At least for him I am still useful, even littlebit hero.
So, out of that experience I can suggest you, if you have a suicidal friend just tell him/her how much you like and need him/her. Don't try to convince in uselessness of suicide. Just tell how bad you would feel if he or she kills himself.
Somebody asked WHY? You never know that. Reasons can be different. There is no universal reason. And it isn't important in the first aid.
About myself I can tell WHY i wanted to kill myself. I had always considered myself str8 guy. All my family and friends hated gays and so did I. I knew that I liked to peek boys but I thought it will go away in time. With puberty. I was on denial about my true sexuality plus that anti gay environment I grew up. One day I fell in love. With a boy from our neighbourhood. I was still on denial. Other day I went to party. All my friends had girls there and I was alone. Then I realized that it never will go away and that I love a boy not a girl. And that I am gay. That very hated gay I have hated myself. I was very lone with my shocking discovery. I sat in the cellar for a quite long time and was crying hitting my head against the wall. Crying eased me little bit so i was able to return upstairs and pretend like nothing had happened. I started to have depressions that only worsened each time. I felt no purpose, nobody really cared. I couldn't tell anyone. I didn't want to be gay. I hated myself so much! So it happened.
Touch of death added another dimension to life. You either are here, feel, see, hear, enjoy or there is nothing. There are still people who care about you even if you hate yourself so much you couldn't see these people who love you despite all your faults. Being gay isn't a fault of course but you got the point. Hating yourself makes you blind.
If there wasn't that tiny desire to live I wasn't here to tell my story. Don't kill your desire to live! Life will help you to survive, get stronger, better. Death isn't. Death is just a black void, nothingness.
I hope it helps.