Free water. Water from your pump on your farm (any pump on map actually) costs you money. Free water can be obtained by backing the water tank trailer into the river and loading it while submerged. The sandy "beaches" next to natural water formations is the best and safest spot.

Starting Tractors. You have more tractors than you really need. Keep your biggest tractor and then the one with the lowest hours. This will give you two tractors to start with.

Missions. Many feel that missions pay to much for to little effort and shun them. That is your choice in how you want to play YOUR game. Missions are a good (prob best) way to earn cash. In FS19 all you have to do is show up and provide the labor (time). As the equipment is provided to complete the mission.

Do not freak out at high equipment maintenance. An old tractor that costs 5 times as much to maintain as a new one is still very much profitable to run. Don't get rid of equipment just because it isn't shiny and new, only sell it if you genuinely don't need it and have something better.

Working your own fields is a pretty slow way to make money in single player. If you are looking to expand quickly, look to other options, such as:

Missions (tons of easy money quickly)
Solar power / beehives (slow money, but zero effort, making for short days)
Greenhouses (IMHO, a nice compromise between fields and solar, you still have to do a bit of work, but it's not nearly as long and grinding as fields)
Maintenance is paid daily so will be more of an issue if you like to speed up time, if you like to play fast then it is recommended you place some passive incomes to offset the costs, Greenhouses are the best value by far, even if only supplied with water.

Don't smoke near the slurry tank.

Icons beside each type of crop will show if the price of it is higher or lower than normal. Every now and then a special demand will go up at a certain buyer and you can make a huge amount of money if you happen to have a large stockpile of said crop.

You can buy a fertilizer spreader or a sprayer and fertilize your crops after they've been planted to double your yield upon harvest.

The goal of the game is to earn money, buy better equipment, fields, and harvest more advanced crops.