No matter how you get someone's attention, sooner or latter you have to talk to the person. Smiling, eye contact and body language are great, but they are just a spring board to conversation.
Once you have succeeded in making eye contact, you should smile. When you smile, you send the message that you are a happy person, someone who is easy approach, confident, friendly. If you make eye contact, but don't smile, you will send the message that you are cold, critical, or aloof.