As said above, it's not too difficult to make money in New Leaf.
Simply go to your Island around 6 P.M. and catch the beetles on the palm trees. Keep your eye out for some sharks, too. You can easily make 1,000,000 bells in one sitting with some patience.
If you want to make money without going to the island, these are some other helpful ways:
1. Grow an orchard of perfect fruit trees. Selling the fruit adds up big time- just leave sure you keep some trees alone, as perfect fruit trees can die, and you will need to replant.
2. Sell fossils you have assessed.
3. Hit the money rock daily for bells and ore. Ore can fetch high prices, but it's rarer.
4. Save your earnings in the bank for interest!
5. Have you saved up Meow Coupons? Remember, you can exchange these at the post office ABD for bells- 3,000 a ticket.
If you haven't seen it already, this video may provide some extra tips if I've missed a few:
https://youtu.be/EWk-wT9ehYI
Good luck!