I don't know about you, but making other people happy definitely makes me feel happier too. Here are a few simple ways you can make someone else's day a little brighter. Hopefully you'll put a smile on their face (and not by physically forcing it into one).
Call an old friend who you haven't talked to in a while just to say hi and ask how life has been going for them lately. Maybe even make plans.
Hold a door open for a stranger.
Invite someone to lunch or to a movie or whatever else you enjoy doing.
Bring cookies to work or school and share them with people.
Leave a waitress or waiter a big tip.
Tell a cashier to have a nice day.
Let someone know you miss them and/or that you appreciate them.
Surprise someone with a small gift.
Leave a thank-you note for the cleaning staff at work.
Donate to a charity.
Visit an old age home or orphanage or an animal shelter to help out.
Offer your seat to someone when there aren’t any left.
Tell someone you believe in them. Sometimes that's they need to hear.
Encourage someone’s dream or goal, no matter how big or small it is.
Ask for the recipe after you eat over at someone’s house.
Stop and buy a drink from a kid’s lemonade stand.
If someone drops their money (or anything else) pick it up and give it to them.
Make a bad joke or pun.
Tell someone you are proud of them.
Listen to someone who needs it.
Give a hug.
Apologise for something you've done wrong, even if it happened a while back.
Thank someone.
Give someone a smile.
Play a game with someone.
Buy someone something (e.g. a book) they've wanted for a while but have never got round to. Or just get them a small present. It truly is the thought that counts.
Remind someone that you love them and that they matter to you.