A shoe's lifespan depends on three main things: repetition, stress, and care. The type of care depends on the type of footwear, but there are several tidbits and umbrella guidelines for how to make your shoes last longer:
Rotation
As temptation as it may be to slip into the same pair every day, shoes need to rest after every 24 hours. Our feet can produce up to one cup of moisture every day. Moisture wears out the inside of your footwear, shortening how long they can be used. This is especially true for fine leather and athletic footwear. Rotating shoes allow them to air out and decompress. Fresh socks and, for those who feet need an extra oomph, a sprinkle of baby powder beforehand is a plus.
Take the Time
Whether we are in a hurry to go or ready to relax, many are guilty of kicking those trainers off to the side or trying to wiggle their foot in without a horn. For some shoes, like flip flops, it's perfectly okay, however, other types of shoe require a bit more attention. Laked footwear needs to be loosened before taking them off. This helps prevent the upper part of the shoe and the sole from coming apart. The same concept goes with putting shoes back on. Over time, the back-and-forth wiggling motion will cause the shoe to break. A shoe horn prevents this damage from occurring.
Storage / Shape
When they are not used, shoes should be kept in a cool, dry place until they're ready to be used again. A cedar shoe tree helps maintain shape and absorb any leftover dampness. Reusing old, dry newspaper and stuffing them into the shoes works as well. Additional protection from dust and dirt can be provided using breathable cotton shoe bags.
Water Protection / Cleaning
Spraying on a water protector, regardless of what the shoes are made of, will keep moisture from penetrating. If leather shoes become wet, wipe them with a cloth, and then let them dry completely at room temperature; heat will shrink them. DO NOT put your shoes in the washing machine. Instead, use a scrub brush, mild soap, and cold water. Shoes made of more elaborate materials, like leather or suede, need to be treated as soon as they get stained.
Other Actions
Avoid dragging your feet or kicking rocks
Shoes last longer by getting the right fit
Even though a shoe's lifespan can not be exactly determined, there's no doubt proper care will extend how long they last.