If your house has a dog door, do let the sitter know whether you close it at night or any other time of the day. Obviously, if she has closed it at night, she will have to open it in the morning. You may note this in writing once. Do not mention this detail five times in the notes you leave upon your departure. The operation of a doggie door is not rocket science. Do not spend an entire paragraph on opening and closing mechanisms. If you do, your sitter has my permission to publish your Unabomber-nutty missive on Facebook. Which she will.
Food and water instructions are important. This includes where food is kept, where water bowls are stationed, inside and outside, how much food should be given and when. If your darling is allowed treats, you need simply to tell your sitter where they are kept and give her some idea of when baby expects a treat. Do not describe the baskets of treats as a "veritable buffet" nor write an essay on the digestibility of a pig's ear versus a rawhide Dingo. Like leaving the words to favorite lullabies in your nanny's notes, this is too much information and behind-your-back-parodies will result.
Dogs poop. Some amount of information must be shared on when and where this is preferable. This is not a term paper. Telling your pet sitter how to pick up poop is insulting -- telling her how to pretend to pick up poop so the neighbors will not scold her is...well, just provide plastic bags and the times your dog is used to being walked and let her conscience be her guide. Trust me, the dog knows what to do when he gets the opportunity and so does the sitter. That said, if your sitter is a teenage boy, you probably should ask him not to discard the poop baggies in the sewer, neighbor's bins or kitchen trash can. If he doesn't poop scoop and gets called out by a neighbor, it's a great life lesson.
Do not call your pet's preferred sleeping spot her "bedroom." At least not in writing. (My goal here is to help you avoid ridicule. If you can't limit your separation anxiety, do limit the proof.) Do let your sitter know where your pet sleeps. If the ritual of putting doggie dearest to bed involves pet toys, blankets or the shutting of doors, be concise. No diagrams. No cartoons. Trust that your pet sitter and your dog will manage to communicate with one another. Whatever you do, do not write a page on how a sitter should interpret a variety of whimpers, barks and scratching patterns emanating from the dog's bedroom.
If you have trained your pet with a hand signal or verbal cue to go to her bed/corner/kennel, by all means do let your sitter know that word or signal. But if you find yourself trying to phonetically spell a sound your dog makes, you have crossed the line. Maybe more than one.
It is not crazy to ask a sitter who is not staying at your house while you're away to schedule in a little play time. That said, do not, do not, describe in writing a game that involves telling her how to throw a stuffed raccoon while hiding behind the couch.
Very important: Do leave a contact number for your vet and perhaps for a friend who can take over should your pet sitter be called away by pets or children of her own.
Be sure the sitter has a house key and knows where the leash is kept.
Your pet will survive. Relax, enjoy your trip. As with children, your pet is able to communicate far more of what she needs that you think, needs far less attention than you think, and will look forward to your return while enjoying the diversity of the break. If you handle things right, your sitter and your dog may bond. This will make it all the easier to leave next time. Just remember: Pets can handle a lot of demands. Put-upon pet sitters may be far less forgiving.