Everyone in here is acting like its immpossible to have a bad trip, so you wont think of having one... but its possible...

Only happends to weak minded people, or paranoid people.

I've only done mushrooms, but one thing i know is Be in a good minset for the trip, and be around things your used to (trip somewhere your familiar with, whether it be you home, backyard... whatever)

Also for the trip, you should have music, and toys you like at hand... it will help you stay in that good mindset.

Also, if some hallucination startles you or something... just laugh it off, like you would if your freind came up behind you and scared you.