Established a useful new habit

I slightly improved my writing, esp. of letters, by conciously using more positive terms even for critical points, sandwiching negative points and adding specific examples (not always three, but I trty to think of at least one).

Decided to behave in a different way in some set of situations

Triggered by lament by my ex-wife I decided to change my routine for change-over of the children. Even though it requires some extra work on my side I think all involved will profit from it. She because of less uncertainty on her side. The children by increased reliability and I indirectly by reduced stress.

Optimized some part of a common routine or cached behavior

As mentioned here I used CBT to get rid of one bothersome habit:

Consciously pursued new valuable information about something that could make a big difference in your life

Locked up joint custody rules and found out that they are not to my advantage. Previously the consequences were a looming threat for my ex-wife and I hope I could reduce her fears by forwarding her some links in this regard.

Learned something new about your beliefs, behavior, or life that surprised you

Went to a disco with collegues after a christmas party. This was basically the first time I have been into a disco and actually perceived how this works. I had great company and even though the disco wasn't that great I learned some disco steps and most important perceive this more fully.

Tried doing any of the above and failed

I tried to start a projects group "systems" in junior high school to pass on systems thinking in a practical and easy way. But I failed to attract interested pupils despite really interesting material (I think).