If you want to increase the number of joyful moments in your life, give yourself more of them.
That list you have in your mind: the things that make you smile, happy, bring you joy; could it be updated or even expanded? It's not about deserving, it's about discovering. We can each build and maintain a relationship with ourselves without thinking we need to 'earn' it first.
Each time you do what you enjoy, you release 'feel-good' chemicals in your body. These chemicals can support you to feel happier (endorphins) and have healthier relationships (oxytocin). Allowing ourselves to explore and experience, without judging the outcome or our performance, can develop motivation (dopamine), mood regulation (seratonin) and creative problem-solving abilities.
New experiences can also enable us to expand our views on ourselves (and others) and sometimes expand our skill set. Take singing in the shower; it may lead to singing lessons, joining a choir, experimenting with Mantra Meditation, or starting and coordinating a monthly jamming session with friends or those living locally to you.
And if it doesn't feel good? Try something else. Refine your recipe for joy until it's to your taste.
Have fun, stay open, and in your moment of joy know that life is not a reward; it's a gift!