Fan-forced air with a heater This type of unit will have a fan which moves air over a heater coil. I much prefer them because there is very little to break. Generally The fruit should be firm and not overly ripe. All blemishes should be removed. I've stoped doing this since it seems unnecessary.
Some apples have a bland taste when dried.
Bannanas Simple cut the bannana into thick slices. Pears I cut pears in half and then cut thick slices. In some pears it is very easy to remove the core and in others it is very hard. My fruit trees web page has comments about that. I leave the skin on.