I've always a had a default setting of negativity. This has sometimes developed into depression. Over time I've learnt to break things down into small chunks.
So if a sink full of dirty dishes seems overwhelming, I'll wash one cup.
If taking a long walk seems like too much, I'll take a walk around the garden.
If I can't face getting out of bed, I'll say to myself, "I'll count to ten then I'll sit up". Then after I've sat up, I'll say to myself, "I'll count to ten and then I'll put my feet on the floor". And so on until I've managed to get dressed, get properly vertical, made a cup of tea.
During the day I'll try to do something, anything that makes me feel better. If I'm out with the dog and see a bit of litter, I'll pick it up. Sometimes I'll pick up two bits. Some days I'll put a bag in my pocket and pick up more litter.
One thing I find really helpful for making me feel better is to help someone else do something. Anything. So today the cook in my cafe (my day job is running a cafe/deli) was under pressure because she had too much to do. So I asked her if I could prep the veg for the soup. Just chopping carrots, leeks and potatoes. It took me about 20 mins to do enough for 20 litres of soup but it took a wee bit of heat off the cook. I felt good about helping someone and she felt a bit less under pressure.
A couple of others have mentioned writing something down at the end of the day, something good that has happened that day. I do that quite often. I get a sheet of paper, split it into two columns. One is "Good Things That I Did". One is "Bad Things That Happened". It's a good sign off to the day, it kind of puts it to bed.
Before I try to go to sleep I also like to make a small list of what I'd like to achieve the next day. It's often very basic - something like...
1) Get out of bed
2) Go to shops for bread and milk
3) Sweep floor
4) Take dog out
5) Phone xxx
If I do these five things the next day then that day has been a success and anything else I do is a bonus.
I do that sort of thing a lot... break things down into manageable chunks.
And I try to always keep in mind that any bad feelings will pass.