Find ways to amuse yourself in everyday life. Find out and come back to things/perspectives that you genuinely find funny. The more “basic” they are, in that you see them very often, the better!
Here are some examples: I find birds dorky and I can’t help but laugh at them. The way they look physically and how they walk with their heads bopping is so funny to me, haha. Another thing could be: just looking at humans and seeing them as these weird creatures, or monkeys. Imagine you enter the perspective of an alien who doesn’t know anything about humanity. The daily behaviour of humans is actually very funny – like, what the fuck is everyone doing?! Really try to enter this perspective, I recommend it. And lastly: people getting worked up over petty things, like getting angry over traffic. I can’t contain my laughter when I see it.
Know what you find funny and have these amusing ways of viewing the world at your disposal. Also, just be aware of what type of humour you have, and then surround yourself with memes/objects aligned with that humour. You can set your funniest memes as your phone wallpaper, or even print them out and stick them to your wall. Or buy yourself a T-shirt with a slogan that genuinely makes you laugh. Seriously, amuse yourself!
It’s important to have laughter in your life. You can make a deliberate effort to bring it in and lighten yourself up in the long-term.
P.S. How to find out what you find funny? Primarily by being observant. The more aware you are of your surroundings constantly, the more little things you’ll notice, some of which are bound to spark laughter in you when you then think about them.