There are 3 main types of pillow. I shall look at each one.

Synthetic Pillows

These pillows will carry the manufacturers method for cleaning and this is your best course of action.

Feather pillows

These can be washed by hand with warm soapy water. Do not rub as this will damage the feathers, instead squeeze gently and then rinse well. Once washed a feather pillow should be hung on a line, shaking often to ensure that the feathers do not become too matted.

Foam Pillows

You can use the same method as for feather pillows except a foam pillow may be laid out flat after washing. You can also have some succes wahing foam pillows in your washing machine, however it is a good idea to keep their covers on. The covers will prevent fraying. Always dry air foam pillows, NEVER in a hot dryer.

General tips

To rejuvenate a feather pillow.
Tumble in a cool dryer for about 10 minutes. To make them really fresh then add a cloth dampened with fabric softener to the dryer.

Another way is to freshen up feather pillows is to put them in a tumble dryer on a warm heat setting along with two or three clean tennis balls.