My opinion is, the most important part of copywriting is
the INTERSECTION where your promotion meets the person you are writing for.
Which is why I suggest that as the starting point for your copy.
Where does that happen, and how do they get there?
If your copy is on a web site, what is the source of the traffic, how did the person get there?
Organic Searches? Links from email? Websites, ads whatever?
If know how they got there, and what is on their mind at the time, THEN you write your headline to match with their preoccupation.
We know we only have a few seconds to capture their attention and less than a minute to go from attention to interest. During this critical minute, they are looking for an escape hatch, a way out, a REASON to leave and they too often find it quickly.
IF you have written to this person in a way which resonates with them, and use your skills to get them reading, watching or listening for a period of time...then you have a chance of getting them to the end.
They will skim the written word, going in the F fashion, left to right, left side down, scan right and so on to the offer or conclusion...
YOU knowing this, can construct your promotion in a way which helps them and yourself too.
So, that is what I think the most important part of copywriting is, what about you?