Exercise helps more than I could tell you

Personally I started writing how I felt. I date it and I'll put the paper up somewhere. I find that having a way to let it out even on paper calms me

Writing how you feel really helps, and forcing yourself to spend time with people who used to make you happy does too :)

Dream journals. Change the ending of your dreams. Like give yourself control.

I like to take a short walk outside in the sun to get a little vitamin D and then come inside to get something nice and cool to drink and then I play music that makes me happy. And sometimes if I'm by myself I'll also play the music really loud and I dance with my dog until she's annoyed with me and sing really loud and slightly off key and just watching her put up with me makes me feel better. And other times when I don't want to get that crazy I'll do things that make me happy like having hot coco and watching cheesy hallmark movies or watching a comfort show even if I've seen it a million times before.