Attract your viewers eye. 
One of the best ways I have found in attracting people to my booth has been through the use of bright lights. This can be accomplished by adding a few extra spots lights, a strobe light or some other type of light to attract your viewers eye. 

Don't be a palace guard. 
The worst mistake you can make is to cross your arms or place your hands in your pockets. Instead, you should hold a small piece of paper in your hands. It will give you better posture and will make you look more approachable. Also, do not stand in the center of your booth. Stand off to the side near the front corner. This will create a less imposing and more inviting appearance. 

Show new products. 
People are always looking for something new. Create a separate sign with "new products" on it. The word "new" stops the viewer's eye and causes a double take. 

Use giveaways. 
Giveaways are a great way to get attendees to your booth, but randomly stacked on a front counter will only tend to create the grab-and-run mentality. It is always best to place them in the middle of your booth. Where they can be seen but the attendee must enter your booth to access them and allowing you the opportunity to make a sales pitch. 

Create a browsing area. 
Attendees like to be invited to an exhibitors booth and the best way is to have open spaces that allow visitors to browse. Create a sign, "You're welcome to browse and enjoy our exhibit." Never place a table across the front of an exhibit, it acts as a blockade and keeps visitors from entering your booth. 

Get the attendees name. 
Never allow someone who has entered your booth to leave without getting their name, address and telephone. I  find the best way to accomplish this is by directly exchanging business cards.