Earning Bells is one of the most important things to do in Animal Crossing New Leaf. There are many ways to get Bells.
The easiest way to earn Bells is selling. The player can earn over 10,000,000 bells by selling turnips, furniture, wallpapers, flooring, clothing, ore (gold, silver, ruby, emerald, ruby, amethyst, sapphire, etc.), bugs, fish, shells, diving, fruit, tools, and fossils. Any item can be sold for bells except for rotten fruit, fake art, and lost items. Also, Re-Tail gives more bells than the Nooklings, so keep that in mind.
Sometimes when the player shakes trees that don't have fruit growing on them, 100 Bells will often fall from the tree. Beehives and certain furniture can also fall out of trees.
Another easy way to earn Bells is probably the most dangerous. When one goes to another player's town (someone who is trusted by the player), he/she should drop all the money on the ground and tells the other person to end session. At the 2nd rotation of the spinning thing, the player should flick the wireless switch. If the other person doesn't receive an error, then the glitch worked. Then the player should go back to that town and pick up all his/her money. The player should have twice the Bells now. On rare occasions if it doesn't work, all the Bells could disappear from the other person's town.
Every day in a player's town, 1 randomly selected rock (not selected by the player) will have Bells in it. If 4 Bell bags are hit out, the player gets 16,100 Bells. But if one has bad luck (tripping with no King Tut's mask), the player will get 5 Bell coins and 3 Bell bags. A good way for the player to always earn 16,100 Bells is dig 2 holes or plant 2 bushes behind the rock right next to each other and put his/her back in the space in between the holes or bushes and rapidly start tapping "A", but without moving the circle pad. Lastly, when the player gets a silver shovel, (rarely) ore comes out of the rock.
When the player gets a golden shovel, the player will then have the ability to plant bell trees. Planting Bell trees is the same as planting a fruit tree. If one buries 1,000 bells, the player will get 3,000 bells in return. 3,000 bells give 9,000. 30,000 give 90,000. The maximum amount of Bells that can be received from Bell trees is 90,000 Bells.