Growing plants and selling the crop is your main source of income during most of the game. Therefore, it is good to remember that it is not always advisable to sell the product no matter what.
First of all, you have to control and compare the prices in the shops. They change every hour. Sometimes, the differences are small (10$ - 20$) and are noticeable only when selling large amounts (however, at the beginning of the game, even such small differences may matter). In most cases, a given shop offers the highest price for one type of product and the price for the rest is unsatisfying. Therefore, always check and compare the prices, as you may encounter 70$ - 100$ differences. Then, with such a small amount as 10t, you can earn 1000$ more. Think about what will happen if you start transporting crops that are a few times bigger. Pay attention to the price changes (a green arrow represents a raise, a red one represent a fall) and you will be able to earn more for your work. You need only a little effort and you will be able to get rich faster. Remember: never sell crop without checking the prices first. You can do it using the PDA [I].
You will also frequently encounter a situation in which some shop announces increased demand (you will be notified with a proper window). It is a perfect moment to sell the supplies from your warehouse or silo. The prices can be even two times higher than usually. High demand lasts for a given period and only one shop offers the increased price - it is marked on the minimap. In your PDA, you can check how much more you will receive for the product - 1, 3 times more may not be enough for you and maybe you want to wait for a better offer. High demand doesn't apply to the whole offer of the shop, but only to one product.
Remember also that you can save money when buying new machines. Shops may announce promotions on particular models and you will receive a notification on the screen. Some of the machines will be cheaper for some time. If you've planned to buy something, you won't get a better offer.
Don't forget to sell the equipment directly, i.e. leaving it in an appropriate spot near the shop. You will then receive additional 20% (normally, you can sell machines for a half of their price, so add the 20% to it). As you can see, managing your finances right is as important as hard work.