TROPICAL - I did acid a fair bit in my youth, but have absolutely no desire to do it these days. Its one of those things that is best done early-ish in life when REAL LIFE RESPONSIBILITIES AND CONCERNS are at a minimum.
Fuck spiritual enlightenment, it wont happen. Cool things will happen, you will think entertaining thoughts, see some mad patterns in things, realise the world is for the most part a ludicrous (yet comforting) charade... but as to getting closer to God or anything like that...ITS ALL BOLLOCKS.
the most important thing is make sure you are somewhere 'safe' with people you know, like and trust (ie dont do what me and me mates used to do, like walk into the centre of town on a saturday night. either stay in or go and sit in a nice park or the countryside or summat)
if you're experience is anything like mine, then...
Expect to feel kind of weird and uncomfortable in your own skin
at some point
Expect to have a point in time several hours in where one of your party says (half seriously) 'this .....will end, right??'
Expect to have a several involved conversations with yer mates lasting several hours deciding whether to go and sit/stand over there, or remain sitting/standing over here. If you do go over there, your party will split into 2 warring factions, the 'I knew we should have stayed over there' lot and the 'no way! its much better over here!' chaps.
if you consume any booze/dope, expect to think 'I can't tell if I am drunk/stoned or not' for several hours, until you realise that yes, you probably are, a bit.
make sure you listen to some seriously monged music
you mantra shall be 'its only the acid, its only the acid'
dont start thinking about your normal straight bread-head square existence man. Because if you do, IT WONT MAKE ANY SENSE
I only had one 'bad trip' and that was only because 2 policemen decided to come and have a nice conversation with me about what exactly I thought I was doing. My answer lasted several hours and covered an expansive range of subject material as I recall.