A customer has just walked in your business. Pause on what you're doing. When you're 10 feet away from the customer, make direct eye contact. When you're five feet away, verbally greet them. This is the called 10 and 5 Staff Rule, this rule is critical! You only have a short window of time to make this effective and the customer needs your full attention.
Offering a warm and friendly greeting is great but a smile takes it to the next level. A smile sets a positive tone, establishes rapport and initiates trust. Smiling lets the customer know that they have been acknowledged and your business is ready and willing to go the extra mile.
Ask the customer how their day is going. Ask them if it's their first time at your business. This is a good time for you to "read" the customer and to see if you can support them in any way. Be sure to actively listen so you know how to best meet their needs. If they need help finding a product, walk them to the aisle. If they're not sure exactly what they need, probe to see what they might be looking for.