Routine, a good diet ( I recommend buying magnesium for your horse, just as a supplement for all horses but I notic eit dies improve their mood), don't always work them; hack do all of that. Keep them happy, healthy, I think their moods are normally better when they're outside often, and just be patient! We're not all blessed with saint mares!
Oestress helped my previous mare. Vet recommended turning her out for 3 weeks in spring and autumn because she was so bad but i couldnt as she was a competition horse and I tried various mare supplements bit of stress was the only one that worked well on her.
Patience and understanding. We all can be moody. Human and horse. Give your mare some space. Don't get mean just try something different. On moody days I keep training short and do things she likes. She loves walking through the trails on property and I practice my heels down and position. Good luck.
If it's really bad regumate helps a lot
patience. kind of think of it as if you were in their position