Preparation is everything

Find out all you can about the company, its products, services, accounts, position in the marketplace and how it's developed over the past few years.
Visit the company's website.
Look through the trade press to catch up on any recent news or check on the net.
Research the job specification if there is one and match your skills to the requirements.
Be prepared to talk about your skills, successes and achievements, so have in mind some case studies you can run through.
Prepare plenty of questions to demonstrate your genuine interest in the role and company.