It’s very possible to increase yours, even without the feeling that it’s hard work.
Pick something that you have an interest in, are curious about or have a passion for or simply recognize a natural talent that you are fortunate to have. Then immerse yourself in it, to learn more about it with a goal to understand it so well you can actually explain it to others.
By simply learning about something you enjoy and have become good at it, even an authority on the subject, you have just given yourself a free education.
Sharing your new knowledge and experience is evidence of a new level of intelligence. It will be seen by others and appreciated too. Now imagine the outcome if you continue this learning loop. It makes me wonder how smart any of us can become simply by learning through experience.