The basics of farming
You should know the basics by now, but in case you're unaware, here's how things go.
First, you clear the land.
Next, you till the soil.
Now sow the seeds.
Use the watering can the water the seeds.
Repeat the above step every day until you have crops.
These are the basic, short version, of how to farm in Stardew Valley. Good, now that's out the way, there's much more to learn…
Not all crops take the same amount of time to grow, and if you want to be getting money from your crops every day, the easy option is to of course plant crops continually.
If each day you plant 10, 20, or even 30 seeds, you'll have something to harvest every day, keeping the money rolling in from the shipping box, and making sure you have cash for everything.
Also try to separate different kinds of seeds, so you roughly know when each crop will be due to harvest.
Story of seasons
Each season allows you to plant different seeds and, of course, reap different crops. As above, they'll grow in different times, but still require regular watering, especially in Summer.
But one thing you'll want to make sure of, is that you don't allow crops to spoil or go outside of their ideal season.
For example, there's no point in planting a crop which takes 10 days to harvest on the last few days of Spring, knowing it will die come Summer.
Bigger, better, more
But there's multiple tiers to the crops you can grow, meaning it doesn't just stop once they're in the shipping box.
You can make star grade crops, higher quality than other crops, which will sell for more money, making them a worthwhile investment.
The best way to get these are to, of course, keep the crops watered every day. In addition to that, make sure to use Fertilizer, which you can craft or purchase, which will enhance the quality of the soil, resulting in better produce.