I was going to suggest buying turnips, but I think you only get that option once you have upgraded Nook's Cranny. So in the mean time, I would maybe suggest collecting shells by the beach and doing some fishing!
Once you upgrade Nook's Cranny, every Sunday, you can buy Turnips from Daisy Mae where you can potentially sell them at Nook's Cranny for a higher price. It's a bit of a long explanation, but this article summarizes it well with the tips and tricks you can follow regarding the turnip market.
at the beginning of the game, i personally made a lot of money off of fishing, although it depends on what fish are currently available in your hemisphere o: if you’ve unlocked the airport and have friends who play, it’s also nice to sell your fruits at islands with different native fruits!
fastest way period is through the stalk market! daisy mae will come to your island to sell turnips every sunday between 5AM to noon. you can use this site to track turnip prices throughout the week; it will predict patterns and prices for you, and the only pattern where you’re guaranteed not to make a profit is during decreasing patterns. additionally, if you have NSO, you can check out the official turnip prices thread every now and then and see if there are any users opening up their gates for high prices c: good luck!
When you manage to get 10k bells, if you find a glowing spot in the ground, dig it up and plant 10k in there (don't do more than 10k). You will grow a money tree and you'll get 3 10k bell bags off the tree when it's fully grown.
catching bugs is a great and easy way i have a bunch of flowers i can give you if you want to bug hunt. granted you'll go though a few nets (lots of flimsy if you don't have the diy for the good ones) but it ain't bad and you can pop balloons while you are catching so it's even better just be sure and wait until the balloon is away from the flowers and water. when it's raining fishing is the best thing. if you need any tools or flowers i'd be happy to help like i said.
lolz oh np i was the same when i started cuz in NL they spawned wherever but in NH the more hybrid and white flowers you have the higher end bugs spawn like the orchid mantis and paper kite butterfly and others. i was just trying to make purple roses for my friend and planted tons of random flowers in one big area and they just spawn like mad. even lower end bugs are good in vast amounts.I’ve been able to collect many flowers so I think I’m okay on that end. I never realized bugs were attracted to them so now I know where to look! thank you!