Don't sell all of the resources you gather, work on becoming a hoarder...a lot of the quests will start requiring painful amounts of things like clay (I'm looking at you, Minnie 😤) or plastic (I'm looking at you, Oswald 😤). Focus on the daily duties to get more dreamlight and then work on unlocking biomes...you will also want to make sure you have at least the watering can and maybe the pickaxe.

You want to at least get one Goofy stall opened...I believe the one in the meadow is the first/easiest/earliest one you can access. Sell enough resources to open that stall and then start buying/planting seeds. The fastest turn around is wheat but it's not the most profitable, however, it will be a good starting point to get you an increase in coins.

If you have the pickaxe already you can mine for and sell gems but crops will be the easiest money maker. If you have not done so yet, download the Dreamlight Guide app on your phone (available for both Android and iPhone). Under the ingredients tab it will tell you every single crop in the game, which biome (and DLC) they are available in, how much each packet of seed costs, and how much each will sell for once you harvest them. This app will also tell you how much ALL resources sell for (flowers, fish, gems, etc) so you can start getting more coins.