You gain levels by earning XP (experience points)
There are several ways to earn XP:
- Plowing your own fields or plowing for other farmers.
- Sowing seeds in your fields.
- Maintaining your neighbours' farms.
- Purchasing items in the store.
- Producing/loading goods in your facilities.
- Working your friends facilities.
You can also earn additional XP by working for a stranger at market as you will receive a bonus chest when you complete all the work on a farm that you were hired to do. What you earn working for others and the Bonus Chest is explained in
What do I receive for working on someones farm?
When you reach top level you still continue to earn XP for your work and when new levels are released you will automatically go up to the NEW level you reached according to the amount of XP you have already earned.
Note: harvesting fields, whether your own or for others', will gain you coins and crops but not XP points.