You can exponentially increase your own happiness by enjoying the happiness of others. Muditā means empathetic joy, and the pleasure that comes from delighting in other people’s wellbeing, accomplishments and successes. You can open your heart to experiencing muditā by practicing metta or loving-kindness meditation.
Loving-kindness meditation is bringing to mind someone dear to you, then someone you have no particular feelings for, then someone you find difficult, then yourself, and then finally for all people (collectively) in the world. For each, using your inner voice, you extend loving-kindness with this phrase:
May you be happy, may you be healthy, may you be safe, may you live with ease.
In extending this beneficence to oneself, the phrase is:
May I be happy, may I be healthy, may I be safe, may I live with ease.
This opens your heart to caring about people. An open heart is necessary for empathy of suffering and empathy of joy.
There is more information on metta here:
https://www.mettainstitute.org/mettameditation.html
https://dharmaseed.org/teacher/119/?search=loving+kindness
This is a guided metta meditation by Martine Batchelor:
https://insighttimer.com/martinebatchelor/guided-meditations/metta-meditation-3