Keep them dry and off during chores. The field watch and the woven bracelet both last longest kept away from water, soap and knocks — take them off before washing up, showering or anything hands-on. Even a water-resistant watch dislikes hot water and steam, which can draw moisture past the seals over the years.
Wipe the watch, air the cord. Give the watch case and crystal a wipe with a soft dry cloth to clear skin oils and dust, and clean the strap to suit its material. The bracelet's waxed cord should simply be kept dry and aired out — soaking or scrubbing frays the cord and dulls the brass bead.
Wind and set gently. A hand-wound movement likes a steady daily wind, done with the watch off the wrist so you're not straining the crown at an angle; stop the moment you feel resistance. Swapping the strap on the NATO is easy — just don't force the spring bars.
Store them apart and cushioned. Keep the watch and bracelet where they can't rub against each other or against harder jewellery, ideally in a soft pouch or a lined tray. Metal scratches metal, and a woven cord picks up grime fast loose in a cluttered drawer.