If you have apple trees and your level is 15 and up, be sure to get the apples because each apple will give you 7 XP. You can find those advertised apples in the paper, visit those people who have that advertisement, and search their farm for rocking trees with an exclamation mark sign. Click that sign and you’ll get an XP bonus. You can also visit other farms and search their dock for a crate with an exclamation mark sign, click it and survey the supplies you need for an XP bonus.
You can also gain extra 30 XP bonus by feeding your pet cat and/or dog. Buy your pet a house and food (bacons for dogs and milk for cats) first before you purchase them with your vouchers. Your pets also serves as a nice decoration for your farm.