Preparing for your interview
Always thoroughly research the company you are interviewing with. If possible, visit their stores or concessions and make yourself familiar with their product and website as well as and researching their competitors.
It is advisable to do a small project before your interview if the projects in your portfolio are outdated or not to the style of the company in question. Don't go too overboard though as you may be asked to prepare a more extensive project to a brief should you reach second interview stage. Just prepare a few sketches that would either sit alongside or update their current collection. This shows that you have an understanding of the product.
Dress code
Always dress appropriately for the company you are interviewing with. If you are interviewing for the role of Streetwear Designer then a suit isn't very appropriate and vice versa.