Think of an act, a thoughtful, caring act, performed by someone that helped you in some way, an act which was rather unexpected, but which eased things for you. It could be a very small act, but when you think deeply, it was valuable for you at that point of time. Compose a letter to the person describing your sense of gratitude (not just a thank you…) and communicate to him/her over phone/in-person or in writing.