It is one thing to be told to become God-focused people, but usually more impactful is a living example. If you have any doubt that David was such a man, consider his prayer in Psalm 119:88, "In Your steadfast love give me life, that I may keep the testimonies of Your mouth."
What typically drives our prayers? Self-interest. And though John Piper in Desiring God effectively shows us that happiness in God is perfectly compatible with our own happiness, we have to admit that often our prayers fall short of that, boiling down to mere self-interest. Even our prayers for the lost, for many of us, often are not driven by God's glory in Christ's conquering grace but by the deep-seated feeling that if we pray for them, witness to them and lead them to Christ, God will be a bit more pleased with us. Much of our praying, if we're honest, is more about us than about God.
David's prayer in Psalm 119:88 stands out in stark contrast to that. He longs that God, in His love, would give him life. So far his prayer is unremarkable. I've witnessed the prayers of many people in hospitals who prayed desperately for their own lives. Why? Almost without exception for reasons like the following: Because they feared death. Because their families would miss them. Because they wanted to continue experiencing the joys of earthly life. These are natural prayers to pray when our lives are threatened. But David's prayer is supernatural: "In Your steadfast love give me life, that I may keep the testimonies of Your mouth." David wanted life for one reason: that he might have another day on earth in order to say 'no' to his fleshly longings and say 'yes' to pleasing God through obedience. Only one thing could have motivated such a prayer - the conviction that his joy in God's glory through his obedience outweighed his joy in anything else.
Ultimately, every decision we make today will be motivated by the expectation of joy. By God's grace, let's join David in the expectation that our joy will be most fully realized in God's pleasure, making us prayerfully happy to be alive simply so we might obey Him to His glory.