I agree with Will, set and setting is very important. If your a bit worried about a bad trip, dont be. Just make sure you have done everything that is required of you that day, and then maye a little bit more to put you in a positive state of mind. Also phone off in my opinion.
Then good people, place, weather, scenery.
I've had many trips, some where people with me have had a bit of a bad time or in some cases very bad time, but me personally have never had it happen to me. That said, when my girl friend lost the ability to walk on a road in the woods 20 mins walk from my house, i was freaking out a bit. Although im sure i would have been calm exactly if i had been sober, just more intense on a lot of shrooms. To clarify, we had all ( 4 of us) taken some 150 freshly picked liberty caps and went on a wander to a local monument at the top of a hill near my house. Eventually got her home without drawing too much unwanted atention as she kept needing to lie down. When home it took a few hours for her to realize what was going on and where she was. She is however very sensitive all drugs, anyway...
Just always remeber your on drugs, and things will go back to normal, lol. Had to tell that to a few people over the years.:D
Oh and as few variables as possible, not in the center of town for example. A well prepared wilderness trip is the best in my opinion, or locked in your house/ flat where its safe, at least till you find your feet with wichever drug it is.
Peace and safe dreaming