Hunt for beetles! Save a lot to have some capital for turnips, then lurk in the turnip threads to make a killing.
Alternately, you can also do trades, selling either services, flowers, items, or even doodles and forum stuff. I got my first seed money by trading TBT bells for in-game ones ^^;
Go for beetles, the best option for a beginning player.
If you have a good Wi-Fi connection, and can be online a lot, you could consider buying turnips. But you'll have to be flexible when visiting towns with good prices because those players aren't online 24/7.
Try to find a Perfect Fruit in your town and plant it, replant the new fruits and start replacing all regular fruit trees with Perfect Fruits. After some weeks you'll have a nice income. Buy a "trash bin" furniture item from Nooklings or a player to dispose of the rotten fruits. (Don't build the trash bin project)
Beetles used to be my main way of making bells, but I'm moving on to fruits now. I have Bell Boom in my town, and my trees are 90% non-native fruits, so it adds up. ;; Harvesting all of them takes forever, though.
When I do an island trip, I only bring back palm tree beetles and finned fish. You can make 350k+ per trip to the island. I hope to eventually be able to replace that with making most of my money from the stalk market because farming isn't the most entertaining way to go about things, but they both work.
Change to Bell Ordinances and follow like what others said "Hunt beetles at island", then you can earn alot or at least 1mil(if not bell ordinance) in a single night =D
-Hunt for beetles at the island after 7pm! All you have to do is walk at a short pace by holding A with your net. Align your shadow with the palm tree, and let go of A. The beetles on the palm tree are worth WAY more than the beetles on the regular trees. I would recommend cutting down the palm trees on the bottom of the beach, just because the beetles are harder to catch.
-Catch finned fish at the island. Any sharks on the island sells for 1,000s of bells. The highest selling price of about 12,000 for a regular shark.
-Make a snowmam. Since it's Winter (in North America), you can make a snowmam, she is shorter than the Bingo snowman and the SnowBoy. The better you balance her shape, the less snowflakes you have to give her for a furniture item. She gave me most of the ice collection, and I sold three furniture pieces at a time for 26,800. It works if you need fast money.
TIP: If you have your development permit done, then you can set town ordinances. Set the "Bell Boom" ordinance so your items can sell at higher prices.