Guests should always take their cue from the person hosting the meal. When the host or hostess takes the first bite, the guests may then pick up their utensils and begin eating.
This etiquette rule came from the royal courts before the invention of refrigeration. By having the host or hostess taste the meal first, it was an indication the meal was free from spoilage.
A similar etiquette rule is protocol for tasting wine when the bottle is uncorked. The person who ordered the wine should taste it before it is poured for the guests to insure the bottle is not bad.