for myself, TRYING to have fun basically prevents it from happening because then i have these expectations that i’m constantly comparing my current experience to and it takes me out the present. i think you gotta appreciate the good moments when they arise and at the same time, accept that the whole day isn’t going to be one huge euphoric experience
when it comes to solo activities, i would recommend just doing the things you enjoy doing on a day to day basis but spice them up a little- i.e. try a different cafe, take a new route, hang out at a park you haven’t been to before, etc. This helps make the day more memorable and can offer something fun and unexpected
finally i think spontaneity is key! follow whatever you’re feeling in the moment, whether it’s getting yourself a little treat from the corner store, calling a friend, going to see a movie, making a quick playlist that perfectly fits how you’re feeling, etc.