All sound advice so far: Don't worry that you might forget anything during the experience, I usually remember every single detail of my trips for a very long time afterwards but make sure you have some sort of note taking material around - I'm a big fan of jotting notes down on my phone (way more portable than pen and paper). Avoid phonecalls and texting people back and forth
Although combinations can be incredible, just stick to LSD for your first time, just to get a feel for it. I'm a big fan of cannabis, but I've never enjoyed it in combination with LSD; it's different for everyone.
Most important advice at all, more than anything else is: just go with the flow, don't fight anything. If some mad little event happens, just acknowledge it - don't get stuck on 'I'm tripping and I can't believe that just happened while I'm tripping".
Make sure you have a nice big choice of music for you both/all to listen to. Be open to other people's choice of music, if other people are tripping too. Good idea to have pair of headphones and an mp3 player available, should things start getting a bit rough; the option of solitude simply being available whether you need it or not can be a great comfort.
Nature is a great place to be, but so is being at your favourite feel good hang out spot - so a balance is good. Even if it is just going out for a walk through a nice natural area. I'd highly suggest to avoid public transport, crowds, unpredictable people and people who don't understand drug use. In fact, if you're tripping with friends who are also tripping, you might prefer to stay away from non-tripping people all together.
Pick your fellow trippers wisely - Am I comfortable with long silences with this person? How open am I usually with this person? What sort of things do we have divided opinions on and will they come up while we are tripping?
Most bad trips I have heard about usually come about because the person in question takes one blotter/drop - decides after an hour that it's not working so they take more. Don't do this - not on your first time. If you're not feeling anything after more than an hour and a half after taking - don't top up the dose - decide to trip another day.
Taking LSD is not some scary ordeal, where the slightest wrong move will send you spiraling into the dark recesses of your unconscious - just roll with it, flow with it, take everything in your stride, be surprised, be amazed, be euphoric, love each other, be open with each other. LSD is very gentle with you the first time. Godspeed
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