A shot is typically 1 oz. of straight or mixed liquor served in a 1 or 1 1/2 oz. glass. Occasionally you'll see a "double," often served in a (very full) 2 oz. shot glass or a highball glass. At least these shots are obviously large; be careful of the 1 1/2 oz. of liquor shots served in the 1 1/2 oz. glasses -- these can look just like very-full 1 oz. glasses holding 1 oz. of liquor but are obviously 50% more deadly.

Shots are sometimes built, sometimes mixed. Always "slam" a shot by drinking it all immediately; they're usually not worth savoring (those that are can usually be ordered as a mixed drink). Never shoot expensive alcohol; you won't get to appreciate the attributes which make it worth more money. If you want to do a straight alcohol shot, choose a well liquor at a fancy bar or the entry level of shelf liquor at most bars. Occasionally it will be worth buying a higher quality of tequila?, but those are also worth sipping.