Write a testimonial just long enough to cover one laminated page. Take your time composing this - several weeks if required. Invite that person to your home or travel to that person's home. It is important that you do this face to face, not just in writing or on the phone. Do not tell the person the purpose of the visit in advance.
Bring a laminated version of your testimonial with you as a gift. Read your testimonial aloud slowly, with expression and eye contact. Then let the other person react unhurriedly. Reminisce together about the concrete events that make this person so important to you.
If you find this technique a bit 'over the top' you might want to just try building gratitude into your every day life. Begin by being more aware of what you should be grateful for and make sure you thank people when they do something for you or help you in any way.
(Martin Seligman - Authentic Happiness)