Just keep them clean, after every use, and apply good quality boot polish.
I had a pair of the original Brasher Hillmasters, back in the 1980s, and they lasted for nearly eleven years.
The uppers did eventually crack near the tongue area above your toes, but that was down to age.
The soles had lost virtually all their tread, but apart from general wear and tear, the uppers were still in good condition, and blimey they were cosy.
Their still in the garage of my mothers home, and their now used as gardening boots.