I think about it all the time. If one little thing goes wrong, that's fucking it, I want out. But, I can never be bothered even trying. If I could be bothered, however, I'd do it. But I've got a really important friend who would be, in his words, "devastated" if I killed myself, so...I've chosen not to do it.
I don't know about advice for people considering about suicide, if they're intent on going through with it, they'll do it, even if you do give advice. But the main thing is, think about positive things, get involved in life more. I've noticed people give up on things they enjoy, and then the dark thoughts kick in...it's best to keep motivated, somehow.