How do I keep my expectations low, so I am more happy ?

I’ve seen when I don’t expect things .. great things happen and I’m very happy
when I’m expecting them nothing great happens
I want to build an attitude in which i don’t expect great things.
I do want to be happy and successful but i think it will be easier to get there if my expectations are less.
please give advise that what should i tell myself to build such an attitude ?