Before you put pencil to paper, there's some background work to do. You won't be doing it alone, though. You'll have help from the people in account service.
The account folks are the people in charge of an account at an agency. They work with the clients to define opportunities, set budgets and timelines, and do a whole bunch of other stuff. They also help you present the work to the client; and they sell work, too, if you're working with some good ones. Overall, they're the liaison between client and agency, explaining one to the other, running interference, and acting as the marriage counselor when times call for it.
As it is with creatives, some account people are great, some so-so, and some bad. Try to hitch up with the smart ones and get assigned to the accounts they're on. The good ones have the soul of a creative person and genuinely share your excitement over a great idea. They're articulate, honest, and inspiring, and like I said, the good ones have a better batting average at selling your work.
Once you get into the agency business, you'll meet another team member called a strategist. Consider the strategist both a cultural anthropologist and a stand-in for the brand's customer. ...