Cause:

Blocked lint traps are the major cause.

Clean the lint filter after each use.
Vacuum dust and lint from the exhaust regularly.
Vent the dryer properly.
The exhaust vent pipe should not be restricted, and the outdoor vent flap should open when the dryer operates.
Do not leave a dryer running when you leave the house or are sleeping.
Have dryers professionally installed and maintained according to manufacturers' instructions.