Onboard a ship of the Imperial fleet, a first officer acts as public assistant -- and private advisor -- to their ship captain. Although their shipboard duties are delegated to a degree by the captain, their primary responsibility is to act as "fighter co-ordinator", and see to the efficient operation of all squadrons onboard.
A first officer and his captain may be thought of as two sides of a coin... While the captain typically acts as the proxy between his ship and the rest of the Empire (and is the highest level of review for all routine operations onboard), the first officer is an internal supervisor of starfighter squadrons.
Such supervision includes maintaining continuous contact with all subordinate squadron leaders and Bridge Crew Leaders, and the double-edged duty of recommending both awards and corrective action to their captain, where such may be warranted. A first officer is also the primary level of response for routine matters and/or questions voiced by squadron and bridge crew leaders, or other onboard officers who may be having difficulty contacting their commanding officer.
In executing these or other duties, a first officer should be responsive to the shipboard methods & protocols put forth by his captain, as well as to the needs of the crew.