I remember watching lectures by prof. Tal Ben-Shahar few years ago about happiness (yes happiness :)). He also mentioned gratitude, and a ritual of writing down

I remember watching lectures by prof. Tal Ben-Shahar few years ago about happiness (yes happiness :)). He also mentioned gratitude, and a ritual of writing down 7 things that you are grateful for each day before bedtime. Namely, it should increase your base level of happiness. Other stuff he mentioned is having regular physical activity and listening to your favorite music tracks (this is something he called peak experience and it also gradually raises you base level of happiness). But I guess these two are obvious compared to practicing gratitude regularly.