Preparing for a psychedelic experience is like planning a scuba dive on a warm water reef. You should decide pretty much how deep you want to go, make sure you have a good friend or guide there with you, and set your intent with a general idea of what you would like to encounter. There is always going to be a moment of anticipation and anxiousness on the boat before you trade your normal world for this entirely new underwater environment.
Once you hit the water, take a moment to get your bearings but don't resist in letting the weight belt carry you down. You'll find your buoyancy at the desired depth. Don't stress if you are a little deeper or shallower than anticipated, you can handle it.
Then the exploration starts, and no matter what you had intended to see, just enjoy the feast of information available to you. Take note of the chrysanthemum of coral formations and the many colorful fish, but don't worry about chasing them all over the reef. You'll remember them. And if there is a shark, don't worry.
The worst thing you can do is try to get to the surface in a panic. You'll get the bends, and it will take a long time in a recompression chamber to recover from your hasty ascent. Witness the shark, and accept that it is part of your world. Face your fear head on, with open eyes and a calm heart. Soon enough, the shark will swim off.
When you return to the surface, understand that those people who were not in the water with you may enjoy the story, but will probably not really grasp what you experienced. That's okay too. This dive was for you.