Prepositions В/На often go together with the prepositional cases in the Russian language. And they are usually the first topic in Russian grammar that seems easy enough to figure out without extra help because they are the same as in English: "В" means "IN". The coffee is IN the cup - кофе в чашке. "На" means "ON". The cup is ON the table - чашка на столе. So this brings us to the simplest use of  "В" and "На":

"В" meaning inside 

в доме, в самолёте, в квартире, в столе

or "В" with institutions and establishments

Think of them as buildings, and you being inside of a building - it is very easy:

в институте, в университете, в ресторане, в кафе, в школе, в офисе, в кинотеатре, в магазине, в отеле, в клубе, в музее

"НА" meaning ON with surfaces and floors

на этаже, на земле, на улице, на проспекте, на столе, на пляже

But of course, as a lot of things in Russian grammar, what seems so easy in the beginning has some hidden tricks. Because on the other hand, we have...