I forgot to tell you something very important when I wrote about Appreciation Marketing. When you're sending all of those wonderful notes, cards, and letters, under no circumstances should you ever... I mean ever. Ever ever market or promote.
Don't send a wonderful thank you message and end it with, "so that's why I need referrals." Don't send business cards, don't offer a discount for a purchase, nothing.
Gratitude is gratitude and marketing is marketing, don't mix them.
Although we forget about this but human beings have amazing bullshit detectors (dogs too for that matter). So if you send a note that says thank you for hiring me and the next sentence is do you know of anyone who needs an illustrator. That becomes a sales message and no one remembers the thank you.
If you have propaganda you need to send or maybe they asked for more of your business cards or something, send them after you mail your thank you's.