Positive stimuli can be anything you like doing, seeing, hearing, etc. I also recommend ensuring that anything you are watching/doing avoids negative topics, situations, or scenarios. I wouldnt watch a drama, or read sad stories. I want upbeat or happy things to help me keep my trip positive.

Because your mind is being chemically altered it can be difficult to control your train of thought once it starts. So by planning or curating a set of positive stimuli you can help keep those influences on a path you prefer. Id usually start by looking at funny memes, trippy videos, high bpm positive music, fun games that dont go into heavy topics (think casual or arcade type games), and Ive also had fun playing with legos.