OK, so we still have millions of these things in use every day, what will keep them running as efficiently as possible?
It all boils down to two basics, short and clean. Short, that's the exhaust pipe. The length matters because every foot of pipe increases the resistance to air flow. Elbows are worse, each elbow equals 3 – 5 feet of straight pipe. Longer, twistier pipe leads to lower airflow through the dryer. That leads to slower drying and potentially overheating of the clothes. Overheating leads to fabric shrinkage and reduces fabric life.
Too long. And there are screws.
At least this one isn't crushed. Yet.
The door location seems to be slightly more effective, but can still pass a lot of lint. The top mount design has a couple of weak points that allows slightly more lint to pass around the edges of the filter.
Both designs are compromises in terms of airflow and effective lint trapping. A finer mesh would stop more lint but would greatly restrict overall airflow. Most of the lint that ends up in the ducts passes through the trap itself. If you take a chunk of the built up lint in a dryer vent and rub it between your fingers you will see that it is actually very fine particles.
Actual lint, no kidding
For best operation the lint trap must be kept clean. This is the major choke point in the system. The trap should be washed periodically, especially if you use dryer sheets for fabric softening. The sheets cause a film build up on the mesh, reducing its size. Remember, never push the start button until the filter has been cleaned.
Despite the fact that you clean the lint trap you still need to clean the ducts on a regular basis. How often will depend on use, but at least once a year. The best way is to disassemble the pipe from the back of the dryer and where it goes through the wall. Frankly, because of the poorly conceived way dryers are designed this is a real pain and most people won't do it. Get a dryer brush that fits your duct system, most likely 4 inches, and clean it from the outside. Tape the exterior flap open and start cleaning at the end. Do a short length and withdraw the brush and clean it. Run the dryer on the air setting for a couple of minutes and repeat. When you have cleaned as much as you can reach (if it doesn't reach the dryer you need to disassemble the pipe) start the dryer on the air setting and carefully run the brush in again. You may get more lint, so don't put your face near the outlet.
An interesting fact, clothes will dry just fine on an outside line year round. It take longer in the winter but it will work. When it's cold try doing a couple of loads of wash at a time, dry what you need in the next two days in the dryer, the rest can go on the line. Jeans and heavy things may need a little indoor drying time to completely finish them. We bring a couple of pieces in at a time an hang them near the radiators, works like a charm.
So, keep the dryer properly vented and clean the lint trap frequently. Then go to the hardware store and buy a clothesline. Line dried clothes smell better and last longer and you get to go out more often. We have a winner.