Liquor doesn't always get better with age. This graphic from eReplacementParts offers a few rules of thumb for when you should discard spirits and other items in your bar cart.
If the bottle is unopened and well sealed, the base spirits will keep indefinitely. But once opened, you have between six months to a year before the alcohol will start to go bad, depending on the drink. The Kitchn says that six-eight months is the spirit industry's standard for when spirits will start to go flat and lose flavour, but for the average person eight months to maybe a year is probably OK.
Got some alcohol you need to use up before it expires? The graphic also offers a few cocktail recipes.
Belly Up to the Bar Cart [eReplacementParts]