Wtf you found a random bag? Get that shit tested first.
Don't take too much at once. U don't feel it right away. Start slow with like 1 max I would say, depending on your size maybe. Stay hydrated but don't drink a lot at a time. Take sips.
At the end when you are coming down, eat something. You won't want to, but you should. I normally have a glass of oj, a yogurt, and some 5htp pills which help. Oh, and smoke too. That helps.
Above all else, do it with friends, preferably a girl, loud edm music, and something soft, like a blanket
Also I recommend not doing it more than once a month.