A joyful mind is very ordinary and relaxed... When your aspiration is to lighten up, you begin to have a sense of humor. Things just keep popping your serious state of mind. In addition to a sense of humor, a basic support for a joyful mind is curiosity, paying attention, taking an interest in the world around you... Noticing everything. Appreciate everything, including the ordinary. That's how to click in with JOYfulness.
It does seem a strange thing to count suffering as joy, yet there's a truth here in that suffering helps to build one's character. Some of the most beautiful people I know are those who have passed through the flames and come out strengthened. If it happens to clay, why shouldn't it happen to us.