John MacArthur in his commentary on the book of Philippians writes about joy, noting that "Biblical joy [is] the settled conviction that God sovereignly controls the events of life for believers' good and His glory...."
Let's just take some time and meditate on that thought.
Biblical joy is to be differentiated from the happiness of the world. The happiness of the world is dependent on life's circumstances; worldly happiness, therefore, is fickle and fluctuating, always dependent on outside circumstances.
Biblical joy finds its roots and foundation in the conviction that God is sovereign and He controls the events in our lives.
Biblical joy is also rooted in the conviction that God loves us and is working all things out for our good. Our good may not be what we think. According to the Scripture, our good is when "Christ is being formed in us" (Gal. 4:9), in other words, we are growing spiritually to look more like Jesus.
Ultimately, the whole of the "christian life" is not about us, it is for His glory (Rom. 11:36).
Let us live our lives in obedience to God for His glory, and I guarantee that you will experience true Biblical Joy.