the first thing
fixed phr.. A2 Elementary Oxford
fixed phr.. the very first action you take in a situation or at the start of your day.
fixed phr.. a pragmatic marker used to emphasize the priority or temporal immediacy of an action within a sequence.
The first thing I do is make coffee.
Call me the first thing tomorrow morning so we can discuss the plan.
The first thing the investigators noticed upon entering the room was that the window had been left wide open.
Usage
often used with 'tomorrow' or 'in the morning' to mean 'as soon as possible'.
Teaching tip
this phrase often functions as a sentence adverbial or a subject complement; highlight its use in setting priorities in daily routines.
Pitfall
at the first thingthe first thingthis phrase usually acts as an adverbial of time without needing a preposition like 'at'.