Not too much really. I have a lot of carbon steel blades (including 1075, 1084, 1095, 5160, W2, 52100, file steel, etc). It is important to keep them clean (free from acidic fingerprints), and dry. Do not store them in the sheath unless you are sure that the leather was vegetable tanned. Use tough cloth, oil, or renaissance wax (my choice) to prevent corrosion. Look at them at least every six months or so to polish any light rusting that may occur (the edge is particularly vulnerable) and to reapply a protective coating.
If your are going to use them, expect patination and use tough cloth or oil in the field. Never let them rest even overnight in a wet sheath. It really is not as difficult as you might think. Often people that let their knives rust would never think of treating their gun as poorly.
Enjoy it! Carbon steels are grr grr great!
Paracelsus
