The most simple and easiest sales tip in the world is to smile.
A smile is contagious. If you smile at someone, they will likely smile right back at you.
Smiles instantly make you feel happier. It is tough to be in a bad mood when you smile. Try it now. Smile. You will feel better immediately.
How does this relate to sales? People want to do business with those they like to be around; people that make them smile. Since smiles are contagious, if you smile, your potential customer will be smiling too and instantly be in a better mood. They will associate this better mood with you and your products.
In addition, smiling will put you in a better a mood and everyone is a better sales person when they are in a good mood.
Try it today. You have nothing to loose, but everything to gain.
Bonus Tip: Smile on the phone too. Your customers on the other end can hear your smile through the phone.