As soon as you can, upgrade crops. There's no need to save money and wait for better improvement. Upgrading crops immediately is a solid investment that will increase the speed of your cashflow and quickly return the money you've put in.

It is also important not to left out carrots. They grow quickly and are a decent investment, so upgrade them as well.

You can watch the ads to get some bonuses and you should always do it, because it's worth it.

Use any leftover gold to upgrade land whenever you can. It will improve your overall income and can be beneficial in the long run.

You'll want to buy some permanent upgrades because they're most profitable. Plant Food and Insta-Seed are among the best ones you can get.

Of course, it is also a good idea to automate your crops in order to get a guaranteed income even when you're not playing the game.

Save up those gems for when you really need them.