10 tips for sword care

1. Avoid prolonged sheathing: Yes, swords were kept in leather sheaths. But not forever. Sheaths, especially leather ones, have dyes and such that can promote rust in a sword. By all means, if you're hanging out at a Renaissance festival all day, please keep your sword in its sheath. But for storage or wall hanging, remove the blade from the sheath. Your sword will remain more attractive that way.
2. Don't bang your sword around: Despite what you see in a movie when some mighty warrior hacks through a tree with a sword, that's a really stupid thing to do. It could bend the sword, or worse, crack or even break it. Swords are weapons. They weren't made to trim your rose bushes or to whack down that oak in your front yard. That's what axes are for. No period warrior in his right mind would ever have considered using a sword for such tasks except perhaps in the most dire of circumstances. And remember, swords might cost a lot nowadays, but they cost even more back in the day.
3. When storing, coat the sword with oil: You don't have to pour on the oil. Just a light layer will do. WD-40 works fine, as do any oils made for firearms. There's moisture in the air, and this can lead to rust on your sword. The oil helps prevent this from happening. Also, make sure the oil you use is non-organic; you definitely don't want corn oil.
4. Don't touch the blade!: This is a pet peeve of mine. The first thing that inevitably happens when you show someone a sword is they touch the blade. NO! Stop that! Fingers have oil on them, but not the good kind of oil that helps protect the sword. Oil from our hands can actually induce rusting, and can even leave fingerprint-shaped marks.
5. Wax your sword: That's right, I said "wax." This is especially important if you're going to be storing that sword for a long time. Many shops that sell swords and Renaissance fairs will have a special sword wax for sale, but some weapon smiths say a good car wax will work just as well.
6. Dry storage: Don't ever forget that swords rust. And even all that oil and wax you've added might not be enough. To this end, when storing your sword, make sure it is in a dry area without a lot of humidity.
7. Don't sharpen your sword: This is especially true for Japanese swords. It takes a lot of skill to sharpen a sword, and it's a task best left to experts. If you absolutely have to have a sword sharpened, contact a professional sword smith and see if they'll do it for you or if they know of someone who can do it for you. Taking a sharpening stone or a turning wheel to your blade might only scratch up and mar the weapon, but it could possibly ruin it altogether.
8. Already rusted?: If your sword already has rust on it, my preferred way of dealing with this is a little olive oil and a Scotch-brite pad. This shouldn't scratch the metal of your blade, unless maybe you scour and scour really hard. Other folks may tell you to use a copper wire brush or steel wool, but I've witnessed swords scratched up pretty well from such use.
9. What about the handle?: Many sword handles will be made of wood. Lemon oil will help protect the wood and keep it from cracking. If your sword's handle is wrapped in leather, you can clean the leather with a paste wax or maybe mink oil (but keep in mind the mink oil will make that leather handle really, really slippery ... so you might want to opt for the wax.
10. Be careful: You knew this one was coming, didn't you? In the modern world, too many people seem to think of swords as toys. Swords are not toys. They are deadly weapons. Even some cheap, theatrical sword bought for ten bucks has the potential to harm. Remember that at all times when you are handling a sword. You are handling a deadly weapon. Treat it as such. Swords can wound, maim and kill. So, just be careful. And enjoy your sword(s).