EYE CONTACT
Eye contact is an extremely important thing when you're communicating with a customer, it is known as an attending skill as it shows the customer that you're interested in attending to them. You can often see emotion in someone's eyes, so use eye contact to listen to a customer's feelings as well as what they're saying to you.
Effective eye contact is achieved by focusing on the customers face as soon and they approach you or you approach them. Then as the conversion moves on you should divert your eyes occasionally to avoid giving the impression that you're staring.
FACIAL EXPRESSION
Your facial expression shows everyone around how you're feeling, sometimes without you even realising it! You must remember that it does not matter to customers if you have had the day from hell, so you must always ensure you don't allow the stresses of the day to show on your face.
You should aim to always have a happy and relaxed facial expression, with plenty of smiling! However do not forget to adapt your expression depending on the customer you have to show when you are concerned or understanding the customer.