Know your stuff. REPEAT, know your stuff! If you are a Cisco or Datacenter engineer be up to date on your basic and intermediate skills. Be able to think outside of the box and be able to think through a problem. If you don't know the answer to something say that you don't know and don't try to fake it because the person conducting the interview knows the answer. Be skillful in mapping technology to business requirements. Do have lots of experience in front of the customer and a full understanding of the sales cycle. Bring your A game and your most personable personality.