Summarize:

Your pet thrives on routine and before you disrupt it completely, you should prepare them well in advance. Start by adding short periods of separation to your pet's daily routine so they get used to your absence, and the absence of others, at home. You may do this over a period of a few weeks leading up to the back school season so your pet is prepared. For example, you may try to leave your pet alone for ten to fifteen minutes in the house while you go chat to a neighbor next door. Or you may leave your pet on their own for an hour while you go run errands in the area. You should also get your pet used to playing alone, as it will be less strange to them once the time comes for you to leave. Give your pet toys that they can play with on their own or leave them alone with a toy so they can have a solo play session. For example, if you have a dog, you may give them a puzzle game that dispenses treats once they have solved a puzzle or figured out how to open a trapdoor in the game. If you have a hamster, you may put a wheel in their cage so they can run on the wheel to occupy themselves when they are alone. If you have a cat, you may provide a scratching post so your cat can play and scratch to their heart's content while you are away. You should try to minimize the drama of you leaving and returning home so your pet does not get riled up when you come and go. You may try to simply open the door and exit quietly so your pet is not even aware that you are leaving. When you arrive home, you may remain quiet and calm so your pet does not become too excited by your return. Try to get others in your household in the habit of making a quiet entrance and a calm return to the home. This will allow your pet to see your leaving and entering as no big deal and become less stressed by the occurrence.
Add periods of separation to your pet's routine. Encourage your pet to get used to playing alone. Do not make a big deal of leaving and entering the home.