Let me tell you some of the tips and tricks I have used over the years I have had interviews in the creative industry. First and most important, BE ON TIME! It does not matter if they make you wait or have to reschedule do to a long meeting or an emergency, plan to be there 15 minutes before the set time.
Second always bring a backup to show your portfolio, either in a tablet or laptop, or if you want to print out the work you feel best shows your skills, do it as well. Once you have these essentials down think of what you are going to wear.
It might sound superficial or not very important as you are applying for creative industries that sometimes (most of the times) do not require a specific attire for the office. Try to keep it clean, ironed and free of holes! Jeans are okay when you got the job, but not before you do.
What I try to do is wear something I am comfortable in, something that reflects my personal style, and is somehow different or makes a statement so the person can remember me by. It could be a bag, or hat, or accessory if really does not matter what is is, but how it makes you feel.
Keep in mind to research what type of agency it is, what type of clients do they have, as sometime you could have meetings with them and you are not only representing yourself but your company, so they would like to know from the beginning what is the best you have to offer.