I think that in marketing and PR disciplines people often feel they have to be noisy and extrovert. But clients actually want to talk to someone normal. A lot are quiet themselves, and don't want people who are bouncing from floor to ceiling.
A few years back, for example, when I was looking for a job, I was told by a rather abrupt recruitment consultant that I didn't do well in an interview for a role in a pr agency because they didn't think I was loud enough. I went on to get a job with a full-service agency – not via a recruitment consultant – and within six months I'd established myself and won quite a lot of new business. I did it through a considered approach and giving clients rational and good ideas.
You don't have to be the life and soul of the party to succeed. As long as you know secretly inside that you can rise above and outshine everybody, that's your secret weapon.