There will be times where you'll need prompt compliance with an instruction from the pilot. When time permits, you should also include the reason for needing expeditious compliance. The term “immediately” should be used when a situation is imminent. The term “expedite” should be used to avoid the development of an imminent situation. For example:

“Turn left immediately heading two seven zero, vector around terrain.”
“Runway two five right, cleared for immediate takeoff, traffic on a two mile final.”
“Expedite climb through flight level one niner zero for crossing traffic.”
“Expedite across runway one five for landing traffic.”