Exercise - especially outside. Walking or running, or outdoor bootcamp.
Something odd that helped massively was doing something I had never done before every single day for a year. It was a sort of private project to get me out of a rut - I read about someone who'd done it, and did the same. Sometimes it was something very small like ordering a drink I'd never tasted before in a cafe, or walking down a street I'd never been down. Sometimes it was something big, brave or somethingI'd wanted to do for ages. It had a really uplifting effect on mood.
Other easy small things that helped were to create tiny moments of peace or pleasure that sort of pierce the low mood. Play music that is calming or uplifting, feed the birds and watch them or listen to them sing, or watch the clouds in the sky. Focus on enjoying a cup of tea or coffee, on stroking the cat or dog, on having a gentle stretch in the morning or evening, read a chapter of an escapist book or watch an episode of a favourite comedy. You mught feel low again after these moments have ended, but I realised if I put enough of them in to each day they interrupted the low mood often enough for it not to really take hold.
Mini self care projects are good. They don't always lift the mood, but it's good practise to be nice to yourself even while you are feeling down, so focus on easy-to-prepare healthy food, taking time to have a long bath or to shave your legs or cleanse and moisturise your face etc. If socialising feels a biut much, use spare time to book dental or eye checkups or any other medical appointments, or book a haircut. These are hard to do if serious depression kicks in, so it's good to get them done even if you just feel you are going through the motions of self care.