In the creative industries, you'll hardly ever complete an entire project by yourself. You usually contribute just a part. So it's important not to go around your agency acting as if you completely own something and boasting about how much of a genius you are for it.
Even if your part is the most visible (e.g. creative or design work), other people working on the project are just as integral (such as the account exec who brought the client in or the planner who developed the strategy that inspires the work). And sometimes even your contribution may have been inspired by something someone else said to you. For those reasons, you don't want to be seen as idiot in the office who thinks they do everything or that they're work is the most important. Acknowledge that you are part of a team, work as a team and win as a team.
But there is a time where you can exaggerate your contributions. A few years ago, as I was finishing up an internship, a senior creative at my agency told me to go out and take credit for everything when applying and interviewing for my next job. It doesn't matter to them if I claim, in an interview, to have written an extra few of their ads but it could help me out a lot.
So the trick is to understand other people's contributions. That way you can give them the credit when it's due but you may also be able to sneakily exaggerate your role in certain situations too.