During the days of creation
God had a regular practice.
At the end of each day, He'd look at what He made, evaluate it, and see that "it was good."
As image-bearers of God -- called to co-labor with Him -- isn't it fitting for us to do something similar?
Of course, the parallels between us and God are not perfect.
God has unlimited power and sovereignty... whereas ours is limited.
And, our efforts are tainted by sin... whereas whatever He does is always holy and just.
But... to the extent we are faithful to our callings... and participate in His work of renewal in this world... it makes sense that we approach each day with the intent that we'd be able to look back at the end of it and say that what we've done is good.
And, such an approach should help us to live in line with the purpose
God has for us.
Which, I believe, is the only thing that really makes a good day good.