A lint trap test
How many of you wash your lint trap often? I don't mean taking the lint out each time you use the machine, I mean wash it with soap and water. Probably not many, and I learned this trick from a fireman of all people.
Take your lint trap to the sink and run water over it. Do the holes of the mesh get filled with water or does it all just run through leaving no hole filled with a water drop? If you use liquid fabric softener you will have this problem more than without any softener. If the water doesn't flow through easily, air can't flow through as well either and this can cause dryer fires.
Every few weeks take the lint trap and wash it with soapy water and a soft scrub brush (don't rip the mesh) and rinse well. I guarantee the rinse will leave almost none of the mesh clogged, which means the air flow won't be impeded either.
Do this test, it is amazing how true it is!