The weakest part of any knife is usually the tip, which happens to be the most abused part! Take care of the point, and the rest of the blade will follow.
Never throw knives, unless specifically designed for that use. I don't make throwing knives.
Never use knives to pry, dig, or chop. Get a pry bar, shovel, or axe instead.
Do not leave knives and sheaths in direct sun or high heat. Ultraviolet light oxidizes woods and bleaches the color out of some gemstone. Heat bakes the protective oils out of most hardwoods and weakens adhesive bonds. Prolonged exposure to the sun and heat can also destroy knife sheaths.
To clean, hand wash blades when necessary with non-abrasive gentle detergent, rinse well and dry.
Clean handles and sheaths with damp cloth and buff with soft dry cloth. A light coat of Renaissance Wax can bring back luster. Do not over-wax. A very small amount goes a long way.
Do not use any kind of oil on the sheaths; this will cause them to soften, weakening their protective function, softening glues, sealants, and dyes.
Protect carbon steel and stainless steel knives with a light coating of hand-buffed wax, not oil. Oil attracts dust as well as weakens the sheath. Renaissance® wax is the best!
Some carbon steel knife blades are blued. Nitrate bluing is a very thin patina that can eventually wear away, leaving a gray metal finish. Sodium (gun) bluing is black, more penetrating, but can also eventually wear away. These are hot blues; used to temper, lightly protect, or cosmetically enhance the blades. They are rust inhibitors, not rust preventatives. Keep clean and dry, wax as above.
Chemical etching is used in the maker’s mark on my mirror finished blades and for cosmetic enhancement. If you live long enough to polish away the etching without the help of power equipment, you won’t have any fingertips left!
Wood handles usually benefit from a light coating of furniture wax or Renaissance® wax and a good hand rubbing.
Brass and Nickel Silver fittings can be hand-polished with Simichrome® and lightly waxed for protection. It is normal for some scuffing to show on the front bolster or guard, this is where the sheath holds the knife. Polish brass often, coat with wax.
For very long term storage, store your knife with the sheath, not in it! The chemicals used in tanning of leather sometimes react with moisture in the air, leading to corroding of even stainless steels! Condensation even within military grade kydex sheaths can invite corrosion. If you can't keep the knife in the open, dry air, store with photographic quality desiccant in a plastic bag apart from sheath.
Keep knives sharp. Most accidents occur when dull knives are pushed too hard. For sharpening: The Razor Edge Book of Sharpening, by John Juranitch (Warner books 38-002) or go to Knife Sharpening.