I think about everything I have to do today. If it's going to be a really fun day, I'm happy. If it's going to be a dreadful day, I'll be crying on the inside :P. But I do try to stay happy on those days since I don't want it to be a day wasted.
I'm the glass way past half full guy. Once I come to and start brushing my teeth I tell myself "I'm going to dominate today". I get dressed and tell myself over, and over today is going to be awesome!!
I tell myself it's going to be a great day and if it's not, that's what the delete button in your brain is for. Keep the happy moments and thoughts in the front and I continue to make myself happy. I'll never see this day again. So might as well make the best of it.
Sometimes when I wake up feeling low, I try to make myself turn it around. Sorta fake the happy attitude until I genuinely feel that way! Just try to tell myself that negative energy is wasted energy. Obviously though some days you can't cheer yourself up and on those days I think you have to give yourself a break and be a little selfish, put self care first, whatever that may mean to you, having a long bath or watching a movie in bed maybe going for a walk, look after you ya know. Sorry I know this isn't exactly what you asked but I guess that's what I do .... Or what I try to do! Anyway best wishes! ☺