One of the bigger problems with computers are overheating issues. These are a big deal since most hardware actually fails because it gets too hot versus actually getting old and wearing out. Heat will ruin your computer in the long run. If you stop your computer from overheating you will prevent this problem as well as random shut downs that many experience.
If you are running Windows download the application called SpeedFan. This helps you determine the core temperature of your computer. You will be able to tell if your CPU is running too hot or not. Generally if you see that it's in the upper 40s it's too hot.
If you can't use this application, generally a computer that is fairly warm to the touch needs to be cooled down. Every machine will have some heat, but excessive heat is what you are trying to prevent.
Dust out your computer. With a desktop, unplug it and dust out the inside. Also be sure to get the vents especially with a can of compressed air. With a laptop get the vents as good as you can.
Get into the habit of never blocking your vents. Desktop computers sometimes have poor airflow when shoved under desks and pushed against the wall. Laptops should never be left on a blanket but always on a hard surface for airflow.
Add more RAM to your machine. This helps the CPU to not have to be active all the time as much lowering temperature and boosting performance by default.
Get a laptop cooling pad if your notebook is a bit warm. This cuts down on it's internal heat and makes it more comfortable to use.
For your desktop if it's still warm after removing all the dust, consider putting a fan that will blow against it to lower the internal temperature. This might seem strange but it's worth keeping your hardware cool, lasting longer, and working faster.
Computers tend to overheat from time to time. This will kill your hardware and reduce your performance. Learn what you can do that will help cool off your machine.