From A Weak to Confident Communicator - 30 Day Challenge
A word of thanks is the simplest way to acknowledge the other person's value. When you say thank you, not only do you show a sign of respect but also leave a good impression. Though this activity is simple, many people fail to harness the power of thank you and take things for granted.
Today, take the opportunity to thank people for the smallest of things. You can improve your thank you's by saying, "Thank you for ....." whenever the situation is appropriate.
When you add a reason for thanking, your message adds more value than a plain thank you. For example, you can say, "Thank you for helping me with the project", "Thank you for the arrangements you made today".