Joy comes when we have the Spirit in our lives. When we have the Spirit, we rejoice in what the Savior has done for us.
And whoso is found a faithful, a just, and a wise steward shall enter into the joy of his Lord, and shall inherit eternal life.
Comparing [our] blessings [with others] is almost certain to drive out joy. We cannot be grateful and envious at the same time. If we truly want to have the Spirit of the Lord and experience joy and happiness, we should rejoice in our blessings and be grateful.