It is pretty hard to give you any meaningful advice without knowing your experience level, your background, and the agency's goals and style.
I'll give you some pointers.
- Listen carefully and make notes every time you have a meeting or a conversation with other agency people and/or clients
- Never over-commit. Don't let your enthusiasm get the best of your ability to produce and deliver
- Meet your deadlines. My oldest son has had an incredible career for a couple of reasons. He got hired for his last management job because the guy that asked him to join the team said to him, you are the only person I have ever met that is always ahead of schedule and under budget
- Every time you are presented with an idea make sure you can explain what that idea is back to the person that presented it
- Constantly look for amazing and inspiring work by others in the same field and try and figure out how they did it
- Study the masters, and I mean the old masters of composition, design, art, literature, music, and do that by reading books. It is a fact that you learn and retain more from reading a book than you do by browsing the internet
- Manage your time - 90% of the people that I know in the motion picture business that always seemed to have a job but never became industry leaders worked incredibly hard but never took very much time to rest, relax and quietly contemplate what they were doing
- Never assume you know more than anyone in the room. If you are not 100% clear on any point, ask questions
I could go on and on, but you get the idea. If you understand people, history, and art, and you listen to the people around you and try to learn as much as you can from everyone you are working with, you will do fine.