As supplementary reading, see the Erowid page on Dr. Charles Grob,[2] a book called The Secret Chief Revealed by Myron J. Stolaroff (about a famous psychedelic therapist),[3] and The Psychedelic Experience FAQ.[4] The book and FAQ have lots of great suggestions for having positive, constructive trips.
One of the key things you can do to increase the odds of having a good trip is having a trusted, experienced guide or sitter. To that end, I recommend the following sitter guidelines: [5][6][7][8]
[1] - http://www.matrixmasters.net/archive/Playalogues/131-Danfort...
[2] - https://www.erowid.org/culture/characters/grob_charles/grob_...
[3] - http://www.amazon.com/Secret-Chief-Revealed-Myron-Stolaroff/...
[4] - https://www.erowid.org/psychoactives/faqs/psychedelic_experi...
[5] - http://csp.org/nicholas/A59.html
[6] - https://www.erowid.org/psychoactives/guides/guides_article2....
http://www.sigmaaldrich.com/etc/medialib/docs/Sigma/General_...
It's a very interesting book -- I highly recommend it [0]. He's not a strong writer in terms of narrative (I found the book's pacing to be jarring given the intensity of experiences described), but he's very precise and describes some very interesting work, and some amazing experiences had by his subjects [0].