Company parties tend to be rote and so therein lies a fine opportunity to bust out of the literal box and make a party that is particularly fantastic. Take care to add elements of surprise and delight.
For informal/small parties, questions drawn out of a hat, delectable food stuffs, and personal gifts bring members together.
For more formal/large parties, keep attention to the feel of the broader space, that it conveys respect and coziness overall. Be sure to see to the finer details like table arrangements. Seating assignments are everything. Draft a seating arrangement, then ask two people what they think of it–they get to see all the names, who is sitting next to whom. Do not ask questions at this stage, just employ their recommendations.
Keep hold of the objective of the party, which is in essence the kind of gift you want to give, and check-in to see how the party is shaping-up to it.
A party is a gift to many in one shot, and your job as the party maven is to be sure the gift is delivered.