I never heard of writing a letter to a fairy before, but I do know that people would leave a bowl of fresh cream for them to keep them pleased. I'm not an expert on fairies, but I know that there are many kinds of fairies, such as a brownie or a leprechaun. Sorry that I can't help more. Best of luck to you.
Yes I've heard of Letter writing to Faeries. I've tried it and I don't really believe it works. You can attract fae simply by offerings such as bread, honey and milk, fruit anything sweet and nice smelling, or even incense. You can call them outloud or in your head. Dont be rude or offend them as they can be very mean. If you happen to see a not so pretty fae dont be surprised and run, they'll get offended! After they've come thank them, mail me if you want to know more!