When I was young in the advertising business I had the great good fortune of somehow not getting a starting job in an advertising agency. Instead, my first job was as a copywriting in the in-house advertising agency of Bloomingdale's department store.
At Bloomingdale's the ads weren't conceptual but they were plentiful. You might literally have to write and produce 15 ads a week. They might be as prosaic as "Plush, pure cotton towels now 25% off," but you got in the habit of churning the stuff out, meeting with buyers, getting their input, then turning that into an ad.
One time I had an ad to write that required real writing, not just a listing of specs. I labored over this for half a week. By the time I showed it to my boss for approval it was, I admit, a real mess. He said to me something like this, "you've corrected this to death." He then tore up my copy and told me to start fresh.
It was great advice. If copy feels worked over it's probably no good.
That was a long time ago, working at Bloomingdale's. I was there for two years before my portfolio was good enough to get a real agency job--a job I took a pay cut to accept.
It was a relief to leave Bloomingdale's for a real ad job. But I never forgot the lessons I learned there.