Animal Crossing: New Horizons: How to raise your Happy Home Academy (HHA) rating

Interior design bonus

This is one that pretty much stacks with any other bonus. You get an added bonus if you have at least twenty items in that room. Just make sure at least three of those items are on the walls or ceiling.

Functional bonus

Another easy bonus is making sure you have a lot of items that serve a purpose or at least allow your character to interact with it. Anything that plays music, anything you can sit or lay on, something that allows you to get access to your wardrobe, a mirror, a DIY counter, anything that lets your village do something with it. If you have a hard time thinking of a layout for this, just literally emulate a room in your home that you feel comfortable in. I guarantee you it’ll work.