Shrooms vary in potency, but between 2 and 3 grams is usually good, do whatever you want but I would strongly recommend not exceeding 4 grams.
Setting should be wherever you're most comfortable. A lot of people say that shrooms are best outside, and while that's true I might recommend starting in a secure, private place, then maybe walking out to the beach later if that's an option. Definitely go for a walk at some point, but it doesn't have to be anywhere in particular. Cities at night look amazing on shrooms.
I've never had the urge to eat anything substantial while on any psychedelic, but there's no reason not to if you feel hungry. Something simple like a peanut butter sandwich would work better than a more complicated dish. I generally avoid eating for 4-6 hours before taking them, but if not eating for 10-12 hours is a problem for you you can eat something small maybe 2 hours before taking them then maybe something a couple hours after.
For things to do one of the best activities is to talk to whoever you're with, and really get into the more basic aspects of your life experience. Try out anything that comes to mind, silly stuff like Twister or examining works of art, just go with the flow. Have plenty of music, if you smoke tobacco make sure you have a lot of it on hand, and bring water/light drinks.
In general try to make a little bit of an event of it, try to avoid sitting around watching TV, and turn off your cell phone. Forget about day to day stuff.