In no particular order.

Writing a thank you text after visiting a friend

Simply saying you had good time is a nice thing to do and often very appreciated. For some it might even be a sort of confirmation that it was a genuinely a nice time and stops any post-meetup rumination and social anxiety.

Spaced repetition

Using a flashcard/spaced repetition app that utilises the Forgetting Curve to schedule when the flashcard should reappear in your review sessions. It feels very nice committing a piece of knowledge to such a system, you can feel less overwhelmed about remembering things and with the scheduling feature, you can rely on that it will pop up in an appropriate time.

I am very happy with obsidian-spaced-repetition. This plugin makes it very easy to define new flashcards inline with your natural note-taking.

I'm always right

To avoid mixing up who's glass your holding in which hand when offering to re-fill someone's glass of water or similar, always have your glass in the right hand. (From Merlin's Wisdom Project)

Half of a triangle in area is 1/3 its height

When you want to split a left over piece of cake and splitting into a smaller pie-shaped piece is difficult, from the base, cut it 1/3rd from the base.

Shisa Kanko

Point and call when you need to keep track of having done things. I.e. locking the door when leaving your home.