Smiles.

Even if you have nothing to offer someone, just offer them a smile. Most people value and appreciate your smile more than what you could ever imagine.
Someone could fall in love with you not for anything but just because of your smiles... Yeah I know you might be raising your eyebrows now... But it's somehow true..
You can't explain the feeling and excitement a guy would have when a beautiful girl says "one of the things I admire most is your smile"... Ooooh my God, you'd feel like flying without wings.
One of the good reasons why you should smile is that:

It lifts a bad mood.
Just the simple act of putting a smile on your face can lead you to feel actual happiness, joy, or amusement.
Smiling at someone could mean so much to the person . Imagine smiling at someone who is depressed, it could help overcome depression to some extent. This really works for kids. Smiling at a kid who is sad could be just an action to you but to that kid, it could be a lifetime memory.
Kids admire people who smile a lot and when you smile at them oftenly, they love you endlessly.

Smiling reduces stress
Smiling relaxes the facial muscles and calms the nervous system.

Smiling helps us to bond with others.
You can try and experiment this yourself.
Whenever you smile at someone, definitely you'll get a smile in return. Some people tend to get attracted to smiles easily, especially the females. Meeehn! this has worked for me severally. Your smile can help in building a good relationship.
Smile oftenly with your friends, relatives, wives, husbands, and loved ones.