You should not keep the cork wet. The high alcohol content of most distilled spirits will begin to dissolve the cork, which is highly undesirable. They should always be stored upright. This applies to metal screw tops as well, as metal catalyzes the breakdown of organic compounds.
To improve the lifespan, the best thing you can do is keep the bottle in a cool, dark place. While it is true oxidation cannot happen without air, it is far slower without energy present, and reducing light-heat is much easier than removing air.
If you are able to keep the bottle in complete dark and below ~70F, it will last far longer. I store mine in a cabinet in my kitchen, and I have an Islay Scotch that has been open for 4 years and shows no signs of degrading, despite smoke being among the most easily destroyed flavors.
Always void sunlight. UV will quickly degrade the flavor of spirits. While the glass of most bottles blocks some UV, any getting through is extremely harmful.
Something else that can be done is to transfer partially filled bottles into smaller bottles. If you have half of a 0.750L, you might transfer it into 0.375L. This would reduce surface area and the amount of air in the bottle.
If you are committed to preserving a bottle that you do not often use, wine stores sell cans of Xenon which can be sprayed into bottles. The Xenon is heavier than air and covers the surface, preventing oxygen from coming in contact with the liquid. However, this is fairly expensive and will not prevent forms of heat/light degradation other than oxidation