this kind of goes without saying, but you have to get ALL of your 'clerks' being a SALES force. Give them questions to ask the customers. And make sure they make it to a customer within 3 minutes of walking in the door.

I've been to my local gamestop a bunch of times just to see if there were games i'd might want to buy... honestly, i've bought 20% more when a clerk has given me direction on what games to buy, and hasn't been a dick or walked away when i've said "just looking".

On the flip side, if a clerk hasn't even aknowledged my presence in a certain time period (depending on how busy it is), i walk out on purpose, no matter what my purpose of buying is (and type of store).