Meetings and Correspondence
Whether you're a freelancer or employed in an agency, you need to know what you'll be writing about. Sure, you can specialize in certain areas, but as long as you're creating content for someone else, they'll be the ones to decide about the specifications. The more details, the more constricted you'll be, but that's not a bad thing. Having a client or employer who knows what they want and can put it in a briefing is a blessing because it eases up the writer's job and speeds up the entire reviewing process. Beware of those who tell you to "do your thing" and undefined tasks, as you'll most likely find hidden desires and preferences behind them.
Research
"Write what you know" is the best piece of advice you'll get as a writer. When writing novels, the scenery is usually inspired by authentic places visited and experienced by the author. An agency life requires knowledge of multiple subjects, so writers need to roll up their sleeves and inform themselves as much as possible. The research process will gravely depend upon the purpose and importance of what needs to be written. Sometimes, reading a few online articles will do; other times, it's necessary to conduct interviews and pull professional literature from dusty library shelves. Keep in mind that interviews also require further transcribing and editing.
Reading
Our vocabulary is the product of what we hear and read. If you're to be an eloquent author, you'll have to devour books, articles, ebooks, and even movies, TV shows, and podcasts. The more opinions, sentence constructions, and expressions you hear and read, the more diverse and attention-gripping your content will be. No one likes bland paragraphs and sleazy already-seen-before slogans! Besides, it would be a shame to limit ourselves to the same old patterns, especially when languages are so full of potential.
Writing
After the research phase, we come to the meat and potatoes of the job. Or do we? No matter how experienced a writer is, they still depend upon something they can't control: inspiration. A writer's block is notorious for its ability to paralyze authors, giving them no other option than to keep reading or staring at walls until they're ready to create again. In its absence, writers improve their work over the years. In most cases, they'll talk about the same subject repeatedly, twisting the same words in different ways each time. Apart from struggling with writer's block, this is the most challenging part of the job, along with covering subjects one has no interest in.
Chasing Feedback
Even if the author is pleased with their work or considers it done, their commissioners have the last word. Writers usually send the first draft to check if they're going in the right direction before stepping out too far. Once approved, they carry the work to completion and ask for feedback again. After the comments arrive, writers edit and rewrite what's necessary and send the piece back for another review. The back and forth goes on until the paying party is satisfied. The frustrating part is waiting for approvals, as each handoff is often delayed or even forgotten.
Editing
Edits aren't only required when the commissioner or the main editor wants to change something about the piece. Some articles or books contain data that need to be updated, or some new facts come to light that change the statements made in writing. It's also not uncommon for authors to finish their work only to decide they don't like it and then rewrite it completely. This is a tedious business that drives even the most skilled writers crazy.