Beautify the Land is a quest given to us by Bayoo, as soon as we complete his Seeking the Swamp Mandala quest. Interestingly, it is given at the exact same time as the (completely unrelated, requirements-wise) Listening to the Land quest given to us by Magnus.
Assuming you have a few royal coins rattling around, you can complete this quest in record time. However, if you're still working on the Willow the Flower Fairy Unicorn quest given by Bluebelle, make sure that one of the decorations you buy is a Log Bench!
While there's not much you can do to prepare for it (except just keep leveling up), the next quest Bayoo gives you will be Rescue the Pirate Girl.
Get any 4 Decorations