Crafting gives large amounts of EXP.

Gather from your animals daily and keep growing vegetables. Upgrade the paddock and vegetable patch when available and catch more animals so you get more EXP from gathering from them.

Always have your granaries collecting materials. The expedition cost is neutral as the rare materials brought back can be sold for the cost of the expedition (if you were short on currency, which you shouldn't be) and you'll still be getting lots of other building materials in the meanwhile.

Make sure to interact with the signboards for built/upgraded buildings as you don't get the EXP until you do.