Unless you're smoking some of the Great Lakes finest danks, out of a nice bong, cannabis is useless to prepare you for a psychedelic experience.
But here is my 2cents.
I tried LSD a week before Mushrooms. And this was a couple weeks after my 15th birthday. Both experiences being amazing. The 2 hit of LSD (strong too) blew my mind but made the 1/16th of mushrooms seem like child's play. Then A week after that I ate an 1/8th of different mushrooms.
And holly fuck, that was a wild ride. Way more of a blast in the face, haha, you're tripping! That was the night I really learned about mushrooms, was seeing insane visuals, less real then the LSD, but more like cartoons in the flesh. I was hearing alien languages coming from the T.V., and had the best body buzz. I think when you get feeling AMAZING on shrooms it beats the the buzz of MDMA. But that also comes with, when shit gets weird on mushrooms, shit just gets weird. I've been pretty scared on mushrooms before, although it might sound odd, I like it a little. As long as you go with the flow the scary shit usually ends up being totally cool, unless you're in the wrong place. Also, the comedown from the 1/8th of mushrooms had me a wake and crying due to a rough emotional strain on my body from something that happened a few years earlier, but the comedown really helped me get through the situation.
So with that little rant I'll say this. I first did LSD and shrooms when I was 15, but had already been smoking weed for a while, and had been smoking good cannabis for about a year. I'm so happy I decided to take the psychedelics, because I had a lot of fun with them through out High School. I miss the late night trips with a few good friends, all of us not having the responsibility of being adults. That is fun as fuck right there.
I would also say don't try any other drugs before turning 18. Cannabis, LSD, and Shrooms is all you need in High School. Stay away from MDMA, Special K, DMT, and other fun drugs until you're brain is more developed.