Always have enough liquor on hand to serve at least one drink per person per hour. Always keep your mixers refrigerated. This will help you save ice and make the cocktails mix better. Never use a glass as an ice scoop. Fragments of glass can chip off and end up in someone's drink.
Cheap liquors tend to taste harsh.
If you must use cheap liquors, try to use them in cocktails containing fruit juices or cream. This tends to hide the taste. Never shake cocktails containing carbonated mixers unless the recipe specifically calls for shaking. This makes the cocktail taste flat. Most people tend to get intoxicated faster when sitting down rather that standing or walking.