Clean the lint trap and vent tube
Lint gathers on the trap during every drying cycle, hindering airflow as the buildup increases. If the vent tube becomes blocked with lint that escapes the trap, moisture and air are unable to leave. Clear the lint trap regularly by peeling off the buildup, and use a vacuum cleaner to clear the vent tube. If the vent tube has visible tears, find a replacement from a stock of dryer repair parts.
Replace the thermal fuse
All dryer models from the past few decades are equipped with a thermal fuse that may blow as a safety measure when the dryer gets too hot. The dryer then fails to warm up during a dryer cycle until the fuse is replaced. For easy dryer troubleshooting, refer to your model's user manual to locate the fuse, and replace it if necessary.
Inspect the heating element
If your clothes are not getting dry and are cold to the touch, the heating element may be damaged. Remove the dryer's panels and locate the heating element according to the user manual, and replace it with a new, compatible element.