We all want love. The key to happiness and joy is love.
God is love.
Building a foundation in the faith in Jesus promotes joy in that understanding of his unconditional love and provision of salvation are obtained.
Acting as God commands in loving others promotes joy in that we learn to not center our emotions on our personal issues but on treating others as we would Jesus.
There is absolutely nothing wrong with self-care or loving yourself. Scripture commands us to “love others as ourselves” (Mark 12:30-31) and this indefinitely will promote joy. If one cannot love themselves, then they do not understand God’s character and care put into forming us “fearfully and wonderfully” (Psalms 139:14).