Step-by-step explanation:
Here are a few suggestions;
1. While playing the game sell fruits expecially rare ones like fish and shells.
2. By shaking trees as much as possible in the game which would give more fruits which can be sold and other valuable items.
3. It is also recommmmended that you hit the rocks you find since they could be crafted or later sold for Bells.
4. A good way to earn passively is by planting money trees which when harvested could give up to 3,000 Bells.
5. There's an option of using a Bell voucher worth 500 Nook Miles which could quickly give you 3,000 Bells.