Also a horrible idea is to go somewhere really hot (like a poorly ventilated dance club or concert in 100+ degree heat) and take a lot of Molly/Esctacy/MDMA (apparently most people don't even know that these are supposed to be the same thing, though what you actually get on the street is anyone's guess), dancing like crazy, then overheating as a result... and some people have died of this.
Drinking too little water, or too much water without the proper amount of electrolytes while exerting yourself dancing on MDMA can also result in either dehydration or hyponatremia. Some people have died of this too.
Finally, some of the worst ideas are to blindly try some new research chemicals without knowing what they are or what their long-term (or sometimes even short-term) effects are.
Taking the classic psychedelics (LSD, psylocybin, mescaline, peyote, and properly identified psychedelic mushrooms) in a safe, quiet place, with people you like and trust and an experienced sitter is the optimally safe way to go.
Do make sure to identify what you have, though. This is very, very important.
I'm skeptical of this claim, every bad story seems to go along with some terrible decision making, "this was my first time doing lsd i was peaking hard and smoked a 1g blunt" or "i locked my self in my room so my parents wouldn't find me"