The first idea is to hang little lanterns like these. You can light them at night.
You can also have a vegetable garden. It only has too be 2 kinds of plants! these are strawberries
I like this idea – get lounge chairs. They are very nice for summer because they are comfortable for reading and just hanging out.
You can add some chimes too. They make very beautiful music just by the wind.
Get a birdhouse. They are very nice when birds live in them.
These rock walls with moss on them are very cool. They make your yard look like a secret base.
Create a fairy garden. You can buy a little house and fairies. My sister loves them.