well, i wrote to Prince Wills twice or more, like you guys said, just be myself and nothing special in the letters. but one time when it was near birthday, i wrote that if he wrote back, it would be the best birthday gift ever. then i got a reply from his secretary, sayin g that cos he got too many mails he couldn't write back.
another time i wrote to the Queen to say i was so sorry for her loss of her dog, i don't remember the name, but it happened last xmas or the one before. then i got a reply from her lady-in-waiting
both the letters were typed, signatures of secretary/lady-in-waiting are hand written. no pictures or autograph
i'm not sure if my letters are ok, cos i don't know the etiquettes about writing to royals. but i did write HM/HRH on the envelope. but it's hard to address them. shall i call them HM/HRH in the letter? won't it be too formal? or shall i call him Wills? will that be too casual? i don't know
i stopped sending them letters now cos it's costing a lot of postage! but i guess if Prince Wills gets married or big occasions like that someday i would send some gift for them