Laptops do just that--sit on your lap. And if they overheat, it's not only uncomfortable, but it can also lead to damaged components.
According to Business Insider, like any laptop, MacBooks can easily overheat if you're not careful. So make sure the air vents aren't blocked.
Instead of resting your MacBook right on your lap (or bedspread), set it on a book or laptop stand to keep the air circulating.
Also, open your MacBook up occasionally and clean out the dust. Use a Phillips-head screwdriver to remove the bottom panel and blow out any built-up crud.
Don't have too many programs running at once, or too many browser tabs open, which keeps MacBooks working too hard.
Finally, stay out of the sun!