What does it mean to deny oneself? One renounces one’s sins and does penance. One says no to the cravings and ambitions of the self and says yes to God’s will. This is metanoia, a radical turning from self-centeredness to God-centeredness possible only by God’s grace and our assent to it.
Your first prayer of the day should be to ask God to give you the strength to deny self for the duration of the day. Everything in the Christian life begins with that.