>>5475310exercise, gently force smiles (actually proven to increase happiness and enjoyment of activities, I'll find the study if you are sceptical) and do a bit mindfulness (5 minutes a day would make a huge difference, I was sceptical as fuck until I had a near-psychedelic experience doing mindfulness)
Take a certain amount of time a day to do an engaged fun activity. Even if it is really concentrate on an episode of something or a song, just pay attention and avoid distraction for that short period of time.