I have been writing down things I am grateful for each night for a while now. It took time to get started and to find a pattern which suited me. Now it is one column per day in a big diary S gets given each New Year at work.
If I miss a day I just put a dash there, when I come back to it. I don't try to fill up the space. It's usually because of illness or some disruption to my life. That's ok and evidence of the changing nature of life at home, sometimes regular and relaxed, at other times fretful and confused. If I don't have my notebooks in the right place beside me and a pen nothing happens!
Any day now I will get the book Ann Voskamp has written about this. Before I get it I will have a think about how this practice has been helping me. Lots of helpful things in life are deadly simple.