@Elixar
Since I was pinged I will give my insight into this, I've done LSD quite a few times. If your friends are scared of a bad trip already - I would not let them take LSD. I can't speak for everyone, however I did make a few close friends while taking LSD, I am basing what I say off of my experiences.
Myself personally, when I was scared of a bad trip before taking L, the trip was a horrible nightmare, I felt as if I was on the brink of insanity. The fear, and indescribable thoughts I had are not something I ever want to experience again. As for steering a bad trip into a good one, I would highly advise not smoking weed. I don't think there's any guaranteed way to steer a bad trip into a good one. For example, if you read online, alcohol use to fix your trip, or make it more tolerable is a horrible idea. Alcohol works wonders for me, but it sent my friend to seek help after he drank too much on a bad L trip (granted he was using LAD, not LSD).
If you have Benzos on hand, I wouldn't worry at all about taking LSD. I've never used benzos to kill a bad trip, I have seen my friend take a benzo to kill his LSD trip, it seemed to work fairly quick and kill it off. If you don't know what benzos do, they pretty much kill off the fear and panic, no 'revelation of the mind'.
As for how bad trips happen, it depends on the person. I had a bad trip start the second I went on the subway, I regret that to my day. That was the worst trip I ever had, and the last time I took LSD. I will never do it again because of that day. I think as long as you plan activities ahead, to keep yourself distracted, and do things that you know you enjoy - you'll be fine. If you take LSD on a whim, just to see fun shit, I'd say that's a bad trip waiting to happen.
Anyway, if your friends are nervous/scared, don't take LSD with them. Or, if you really want to, have benzos on hand to prepare for the worst.