Instructions
Attract one species of Pinata to the garden and breed it repeatedly until you receive the Master Romancer Ribbon for that species. You get experience each time the Pinata breeds, as well as experience for earning the ribbon. Give Piantas Romance Candy to help them breed faster.
Give your Pinata a few Joy Candies to make them extremely happy. Highlight the crate sitting outside of the garden. Press the "Y" button and select the happy Pinata. This sends the Pinata to a party, earning you experience.
Grow as many types of plants as possible in the garden. As soon as you plant a seed, apply three applications of fertilizer to it. This produces a high quality plant, so you get more experience than normal. Most plants take just a few minutes to grow, so this helps you level up quickly.
Create variants of your current Pinatas. This is often done when you give a Pinata something to eat, like a colorful berry or flower. Feed your Pinata a variety of items to see what causes it to change. When a variant is created, you earn bonus experience.