Alcohol stains are caused by spilled drinks and by many medicines, lotions, and perfumes. Since alcohol dissolves many finishes, it is important to react quickly. Wipe up the spill quickly and rub the spot vigorously with your palm or with a cloth dipped in a small amount of furniture polish.
For older stains use a paste of rottenstone, baking soda or cigarette ashes mixed with mineral oil, linseed oil, or lemon oil. Rub lightly in the direction of the grain. Then wipe with plain linseed oil. Rub briskly with the grain of the wood, using a clean soft cloth. Wipe frequently to compare and match gloss of the repaired area with the original finish.
Powdered pumice (from paint store) is a harsher abrasive than rottenstone. Test to be sure it will not damage finish.
Rottenstone is a very fine abrasive, found in some hardware and paint stores.