At 12:30 on any day, walk along the beach shore looking for fruit. Any fruit you find along the shore can be sold for 500 Bells.
To get more money for fruit, go to your friend's town where, instead of only 100 Bells, you will get 500 Bells per fruit.
Go to an online friend's town, pick their fruit, and plant it in your town. You can make more money from outside fruit.
When Joan the turnip peddler comes to your town on Sunday mornings, ask her if she has Red Turnips. If she sells them to you, plant them right away. Water them every day for a week, then dig them up on Saturday. Red Turnips sell at Nook's shop for 16,000 Bells.
Eventually you will get a coconut, either by finding one or your mom might mail you one. Plant them after five to seven days, they will become trees. Sell the coconut at Tom Nook’s for 500 Bells.
After you plant flowers for Tom Nook, talk to him for your next task. After that, go out and pick up the flowers you planted to sell them back.
Get a Golden Shovel and bury some money in the ground. Water the plant and eventually a money tree grow in the week, month, or year.