A cool computer is a happy computer.
Many of the parts inside a computer get very hot so having good circulation is a big benefit. Your computer will last longer with more airflow.
Dusting it out every year or every 6 months if you have a pet is also good practice as fans will get clogged with dust and animal hair which can cause more heat and/or kill the fans.
The vents on the front, sides, and back of the computer should not be blocked. Many of the computer desks you buy have enclosures for the computers to go in so you do not have to listen to the loud noises from your computer but they actually just makes things hotter for your computer by blocking off the vents and not letting the computer pull in any cool air.
If you hear your computer making any strange noises most of the time it is a fan dying. You want to get that replaced ASAP as that could hamper the performance or even kill off a part inside your computer.
One thing that is detrimental to a computer is smoke. If you or someone else smokes near a computer the tar gets inside the computer and clogs up fans. No matter how much you try and get it out you cannot, it sticks to everything. Smoke is one of the worst things for your computer you could do.
As for keeping a laptop cool you will notice some of the air vents are on the bottom of the machine. If you prop up the back of the laptop by 1″ this will cool it down tremendously. Laptops are known for overheating because of clogged vents on the side or bottom.
This goes for you mac users too.