My approach is simple: I am happy to share what I know if people are curious, I am always happy to give people an idea of what to expect / watch out for as they consider trying a new drug I have experience with, but I don't try to persuade people either way anymore. I used to proselytize more to friends when I fell in love with a new drug, but there's just no point. IMHO, anyone who wants to try / is curious about trying psychedelics enough, at least here in the first world, has more than ample access to basic info on health and safety data, dosage, general effects profile, etc. of at least any common/well known drug. I talk about "drug stuff" and related neuroscience a lot with friends when it seems relevant, but when I'm talking about a specific drug to someone thinking of trying it, usually it consists mostly of informal trip reports and other subjective commentary.
My usual process, I guess, comes in two flavors: if someone is still pretty unfamiliar with a drug I tell them about, I'll give some basic info and tell them to read up on BL/erowid/pihkal/etc. if they're interested and to hit me back with any specific questions. If they've already done some research and are seriously considering trying it, that's when more extensive subjective commentary comes into play. If they're still at the 'believing LSD makes your brain stem bleed' point, I may try to correct their wrong-headed ideas but I won't be trying to convince them to take it anytime soon. Most of my friends know better than that kinda stuff, at least.