It took me while to come to a real understanding of where appreciation leads us. I was always very particular to thank anyone who helped me in any way, but I wanted to understand the depth of being makir tov. What I came to realize is that when you are able to appreciate anything that someone does for you (even if you pay for it) then life is filled with menuchas hanefesh. One realizes all the good HKB”H does, even in hard times.
Thank you cards, small little gifts, returning a favor are all great ways to show appreciation–a personal phone call of thanks is still at the top of my list.