Welcome.
Previous experiance with psychedelics does not necessarily matter...the first time I smoked DMT I turned into a crying mess, I had experiance with most known psychedelics, and the DMT still caused a "freak-out", while a friend who had no psychedelic experiance handled the DMT just fine.*
I would say it's best to not expect anything, this means to eliminate any preconceptions you may have regarding what you think these things may do, enter the situation as someone who is open and willing to learn, free from pre-formed notions of what the psychedelic experiance is.
I have brewed ayahuasca, and some people experienced nearly nothing, and some people were overwhelmed by the intensity of their experience, all from the exact same brew.
Don't be disappointed if it does not happen right away, with San pedro cacti you are consuming mescaline, the goal should be to ingest between 400-800mgs, which is easier said than done. If it fails to produce much effect on your first attempts, don't be discouraged, just keep trying until you get where you were trying to go, in the process you get to learn about, you get to know, and you get to build a relationship with the entheogen.
...on the other hand, if your first experiences are overwhelming, please do not be frightened away from entheogenic exploration. Some times you get more than you want, though often it may be exactly what you need, however just because it was overwhelming or frightening once, does not mean it will be that way every time.
It's a lot like making a human friend, you have to get to know, and build a relationship with these entheogens over time. Some may make bad first impressions, but will turn out to be amazing allies in th end.
These compounds can do many things to many people, and can be extremely variable in their effect, so it's best to listen to others, but to do it with a grain of salt, as their chemicals experiance May not apply to yours in any way.
I would say if you eliminate all your pre-conceived notions about what these entheogens do, and you eliminate any notions regarding what to expect from them, and keep a humble attitude, while remaining open and willing to learn, you will be just fine.
I wish you luck with n your explorations,
-eg
(I posted the report from my first DMT experience simply to illustrate what was meant when I said "freak-out", because while it was an ordeal, and while I did brake down in tears, it was also a very benneficial experience. I did not post the report to illustrate what to expect.
*
Quote:Experience report
*note: the dose range in this report is highly inflated, there is no reason to ever dose this high*
the first time I used N,N-dimethyltryptamine I smoked 200mgs of translucent yellow crystals on top of a small amount of high-grade cannabis, I cleared it in a single hit. I held the hit in for around 5 seconds when the rush began, "I don't believe it!" I kept repeating in my head, "this is impossible".... my surroundings began to quiver and slither apart, faster than anything I had ever seen everything began moving away from everything else in a mash of brilliant color geometric form, and speed, before fully shattering the "reality" in my visual and mental field, it came on like a freight train, I remember thinking "oh fuck! Get this stuff out of me!" And frantically trying to exhale. It was pure terror, I thought "now you have done it! You killed yourself!" After brief mourning at the life I had just departed from I began to pay attention to the present, I remember feeling like I was at the bottom of a foggy mountain with dirt roads, the clouds felt like a domed ceiling, everything was wet, misty, cloudy and rainy, I was overcome with an intense feeling of panic and deja-vu, I felt like a lost child, everything I knew about who I was or my life or earth seemed like a distant dream, like I dissolved out of existence, I interpreted this as dying, I knew that I was dead, and I was emotionally overwhelmed while confronting the event of my death, just like sand slipping through finger cracks my entire identity as a human was dissolved, I remembered my name, the earth, my family, who I was, being a human, but like grabbing at smoke, it was futile to cling to all this, I had to let it go....I could not tell if I was breathing or not, I would take air in, but couldn't feel it, then noticed a pain in my chest, a giant mantis like being had its claws in my chest, it proceeded to tear open my chest and stomach removing all my organs and insides, I was about to go into shock when I saw a bright green light flash over my shoulder, it nearly hit me, it then became a beautiful geometric object, morphing and color changing, like a jewel from hyperspace, the mantis then put this object in my torn up body, he began to make billions of these objects, each one unique and radiating beautiful colored light and the mantoid filled my body with them, then I was sealed up and propelled into an orange light where I was resurrected...then I felt as if I was being pushed through a membrane, I was being born...slowly I began to recognize my surroundings, my face still covered in tears, I looked up and saw the branches of a tree next to me all slither in from all directions to take place and solidify as the tree, the world began to slither back into place, most things moved like elegant but sinister snakes, or like the dancing movements of a flame, as the world constructed itself back into the familiar, so did my conscious state and memory, I was still disoriented, and fairly traumatized, I thought I had been gone for millennia, "how long was I gone I asked?"...."about 20 minutes" was the answer ....those who were there said in reality I curled up into a ball and began to cry for 20 minutes, I was wondering why my face was wet, because it felt like I had actually just went through being born...any way the immense deep spiritual and psychological implications of this experience left me for ever transformed, reborn as a new person entirely, it was the single most meaningful thing that has ever happened to me
-eg