Let your joy be unattached to any particular thing. Consider it a natural state in you that requires no external conditions for its existence. Rather it is the motor that manifests reality for you - whenever you feel able to let it. Therefore when you feel joyful by all means be glad of those circumstances that make it easier for you to feel it, but do not attribute to them the cause or source of your joy. That is you.
When joy eludes you do not blame yourself, for that will keep it locked in its box. Notice that it’s gone missing and trust it will find you again. Go within; move towards stillness. Think of it as a shy creature that only emerges when it feels safe. Your willingness to be permits it to emerge and be with you again.
You are living in a time when intense waves of light are focused upon the human heart. The potential for developing your heart centre in this lifetime is great. And the heart is the natural home for your joy. Every time you feel joy, however momentary or fleeting, your heart evolves.
Sometimes when you feel joy, imagine it as having no boundary; that your joy fills the world, indeed the Universe. Then you may begin to glimpse that the Universe is created out of your joy.