I installed the "Thanks Diary" app on my phone. It reminds me to add a "thanks" every night. I mostly try to write about 3 notes, although sometimes I could only think of 2, while other times I wrote 4 or 5. So far I have written 23 "thanks" in 7 days.
I'm not sure I feel any difference yet... I think that will come when I re-read my notes some time later. :)