When I am interacting with the dog, often his tail wags. This shows his excitement and interest in whatever is happening. When his tail wags, I become genuinely excited because I know that I am doing something he enjoys. I automatically remember whatever I was doing and usually make a mental note to try to emulate the same thing later. The tail wagging of the dog has become something which makes me genuinely excited.
For better or for worse, humans do not have tails to show their excitement. However, we do have words and body language. When interacting with others, never be afraid to show that you are interested. Not only does showing interest make it more likely that more enjoyable things will happen, but it serves a greater purpose of making others genuinely excited as well. Showing interest makes the entire experience of being in your presence even better, which in turn will make your entire life more enjoyable.
Be interested. Just because we do not have a tail to show it automatically, does not mean we cannot show it at all.