There are several decent early-game money making strategies.
The 'best' option is, of course, fishing. You can net an enormous income by going to the lake and fishing all day. If you spend all of the second day fishing, you can get your skill up to at least the point that you can use the next tier of rod that can use bait to further your profits on catfish when it is guaranteed to rain on the third of spring. From there, it snowballs.
This, however, requires that you master the fishing minigame. My carpel tunnel syndrome objects to this. So, there are other, albeit less profitable, options.
First off, forage can actually net you a decent chunk of change. Save one of each foragable for the community center, sell the rest. Maybe eat some if you're working on building infrastructure, but selling is probably going to be the best bet. Second off, a 40 parsnip start is a good way to kickstart your produce production. Basically, take all your starting money, buy more parsnips, and plant 40 on day one. Sure, you might lose a couple to crows, that's the price of doing business, but you'll still be in position to sell them to buy at least one potato and some kale, as well as everything else you'll need for the spring crops bundle. If you've been industrious, you might have collected enough minerals in the mines to have gotten nine Cauliflower reward from Gunther before the middle of the season. That's a heft chunk of change.
Strawberries are also extremely profitable. You can normally only get two harvests from them if you buy them from the egg festival, barring a very tightly timed technique to get 20 speed gro from the community center bundle so you can get a third harvest, but that's not a very easy thing to do. However, even with two harvests, they're still more profitable than anything else you can grow in the first spring. They're worth a decent amount of farming experience when harvested as well.
It's not nearly as profitable as the fishing strategy by any means, but it can get you going as an entry-level strategy.