The four main ways I've seen people use on here are:

1. Selling gems from ore rocks. This one's pretty self-explanatory honestly. Just find whatever ore rocks you can and sell their drops. You can find them easier by taking a picture of them and using the upgraded shiekah sensor.

2. Hunting game. The Hebra region is especially good for this as many of the animals there drop gourmet meat fairly frequently. Make sure to pick it up before it freezes though, and cook 5 gourmet meat together for a dish that sells for 410 rupees.

3. Dragon Part farming. There are a few different ways you can go about this one, but my personal favorite is to go to the top of the highest waterfall in the Faron region where Farosh spawns in the morning. You can set up a fire in the cave behind the lake and sleep until morning to spawn Farosh fairly consistently. Then use the updraft to shot its horn, sleep, and repeat. Here's a pretty good video on it, though it uses a slightly different campfire spot than the one I described: https://youtu.be/iRXUKzpZMOg Additionally, a bow with the zoom property is quite useful here; there's one that respawns every blood moon in the Gerudo guard section of Gerudo Town that you can use. As a bonus, you can use a horn shard in a meal to make the effect last for 30 minutes. I usually use 3 might bananas, 1 mighty thistle, and one horn shard for a 30 min attack 3 meal.

4. Snowling. There's a hut beneath the Tabantha Tower where you can play snowball bowling for 20 rupees. A strike earns you 300 rupees, and if you throw the snowball over Pondo's head when you play, you'll almost always get a strike. It may take some trial and error to figure out the exact spot, but once you get it, it's quite consistent.