Don’t flash an immediate smile when you greet someone, as though anyone who walked into your line of sight would be the beneficiary. Instead, look at the other person’s face for a second. Pause. Soak in their persona. Then let a big, warm, responsive smile flood over your face and overflow into your eyes. It will engulf the recipient like a warm wave. The split-second delay convinces people your flooding smile is genuine and only for them. 
Smiles that are too quick are usually seen as disingenuous. If you allow your smile to erupt gradually into a big, warm smile, you will be seen as much more sincere and personable. The person you are talking to will feel special as if the big smile was made just for them. Over the next few days, observe the smiles of those around you. Who are the people usually seen as the most credible? These people will almost always have a slow, sincere smile.

“People can respond however they want to my flooding smile, but bringing my whole self to work is worth it.”