Check in with someone before you head out to do your errands an ask them if they need anything.
Offer to walk your friend or neighbor’s dog if you know they’ve been busy or frazzled.
Make an extra pot of soup, or pan of lasagna and deliver it to someone you like.
Hold the door open for everyone, male or female, especially of they have a load of stuff in their hands, or have kids with them, or look like they are having a harder time walking than you. Just make a habit of opening the door for whoever is behind you, or next to you.
Smile at the customer service folks, and ask politely, “So how is your day going?” Instead of talking or texting when you interact with them.
Don’t engage in petty road rage shit, even if some asshole cuts you off, or does something else that appears to be done on purpose. It usually isn’t. It’s usually just garden variety inattention. Are they being deliberately unsafe or dangerous? Call the police, otherwise be like the girl in Frozen and let it go.
Plan ahead. The more things you can do, like pack your lunch, lay out your clothes, get the coffee maker ready, have the car gassed up, the less likely you will put yourself in a bad mood, and the less likely you will take out your bad mood on others.
Send a “have a nice day” card to a friend or loved one.