Rejoicing and Thankfulness

How can we rejoice?

A friend wrote this reflection on rejoicing in a New-Covenant context, and I appreciate it. I agree with it. I might even understand it.
But I don't feel I can participate in that kind of rejoicing. Maybe sometimes; but it feels like an Old-Covenant practice. I'm rejoicing because things are going well; because people are happy and problems are solved and life is good.

For a long as I can remember, I've understood the teaching that Christians should be joyful, rather than happy. Joy is a fruit of the spirit, happiness is a consequence of our circumstances. The way I've always applied that, though, is to associate rejoicing with happiness (and circumstances), while associating Joy with thankfulness in spite of whatever might be going wrong, and hope for what is to come.

That's obviously not the right way to go about things.
But I'm having a hard time moving from point A (being thankful for all the blessing I have, in spite of all the grief and pain and sorrow in the world around me, and hoping for a time when all promises will be fulfilled) and point B (rejoicing in the Lord at all times.)

Perhaps I can cultivate a kind of rejoicing in my own life--perhaps I can express joy as a celebration instead of a reflection. That doesn't quite take me all the way, though. How can I rejoice with my friends who are grieving? What would that even look like?
Being thankful, looking on the bright side, seeing the cup as half-full, doesn't cut it. There must be more.

Christ's death was a promise; His resurrection was the fulfillment. Our hope is for today.