I've pondered what this exactly means. To me it means trying to keep a positive attitude, seeing the positive in things rather than the negative and it just builds upon itself. The more positive/happy/joyful you are - the more positive/happy/joyful you become.
Man is fond of counting his troubles, but he does not count his joys. If he counted them up as he ought to, he would see that every lot has enough happiness provided for it.
Not by appointment do we meet delight Or joy; they heed not our expectancy; But round some corner of the streets of life they of a sudden greet us with a smile. ~Gerald Massey
Look at the trees, look at the birds, look at the clouds, look at the stars... and if you have eyes you will be able to see that the whole existence is joyful. Everything is simply happy. Trees are happy for no reason; they are not going to become prime ministers or presidents and they are not going to become rich and they will never have any bank balance. Look at the flowers - for no reason. It is simply unbelievable how happy flowers are. ~Osho