I had this issue one time when group of my friends and I wanted to do a psychedelic ceremony out in nature around a bonfire.

I was concerned because they wanted to dose hard on mushrooms and at least two of them had never done it before. I had tried to make a case to warn them that the experience might be intense but they were insistent on tripping that hard.

So, perplexed with this problem beforehand, I happened upon Timothy Leary's 'The Psychedelic Experience: A Manual Based on the Tibetan Book of the Dead'. In it, Leary does an excellent job of describing the different 'bardos' or stages of the experience and how to work through some of the more difficult transitions. He prescribes certain sayings and visualizations that you can use to help along people who are struggling with a bad trip.

I didn't get the chance to use it since this experience went great for everyone, however it might be just what your looking for. Do a google search and you'll be able to find a free pdf version that you can download and print off for your uses. Check it out!