Mixture of things.
Being outside in daylight, whatever the weather, once a day.
Windows open for at least an hour, whatever the weather, every day.
Going to the gym/pool, especially when I really didn't feel like it, telling myself I'd just do ten minutes and I could stop...just another ten minutes and I'll stop...just another five and I'll...I feel great. The occasional nah, I really can't be doing with this, I'll go and sit in the steam room/sauna for five minutes...oh, I feel like a swim now.
Proper mindfulness meditation run by the Buddhist Centre.
Finding excuses to go on 'pointless' expeditions. Yeah, I could have bought some sushi from Tesco's or the Co-op, but a trip to a specialist supermarket selling all manner of interesting things meant being out and doing 'something' rather than being in and staying miserable. Might as well be miserable outside, get some daylight and the best strawberry daifuku I've ever tasted to eat whilst sitting outside a gallery as the sun comes out. If I was bored and miserable, well, I could do with getting a pot cover for that plant - might as well get on the bus out into the arse end of nowhere to that nursery/garden centre and come home with 5 new plants, two pot covers and a jar of local set honey.
Planning a more effective layout of particular rooms or areas, making sure things were as light and bright and fresh as possible (but be warned, this can end up with painting walls at 10pm whilst you wonder how exactly you got from a new duvet to 10l of Farrow and Ball by 12.30pm).
Human contact. Being out, doing stuff, forcing myself into situations where I'd be around people. Joining a band was the big one, but even attending a choir when really low due to a bereavement really helped, as the music provided an outlet for feelings.
Plants. So many plants. Also a good way to find something to have a conversation about with other people. See also random cooking, galleries and ridiculous decorating decisions.
And, most of all, getting shot of the ex. That meant I could do all of the things without him being there to restrict, control and to drag me and drag my mood down at every possible opportunity.