Most of what shortens a boot's life is not the walking. It is grit left in the tread, and heat used to dry them out.
The routine
Brush the loose dirt off, wipe the uppers with a damp cloth, and let them dry away from direct heat. Smooth leather takes a renovating cream or conditioner. Suede and nubuck need a suede brush and a protector spray instead, never a cream, which will mat the nap.
Keep the soles clean too. Grit packed into the tread wears the sole faster than the ground does.
What to never do
Do not dry them on a heater, in front of a fire, or in a car window. Heat shrinks and cracks leather, and once the fibres go there is no bringing them back. Skip the polish on textured leathers as well.
Waterproofing
Blundstone recommends re-waterproofing roughly every three months depending on how hard you wear them. Somebody on a wet job site should do it more often than somebody wearing them to the office. Under average wear Blundstone expects a pair to last two to seven years, and care is most of what decides where in that range you land.
