Provide a small room with food/litter expanse as a base camp for your cat to initially acclimate.
Dedicate Safe Room
Move bedding and toys bearing the previous owner/foster's scent to offer comfort.
Bring Scent Familiars
Keep feeding times, interactions and other habits predictable to ease uncertainty.
Maintain Routine
Gradually introduce your cat under supervision to other home areas until learned.
Give Them "Tours"
Take introductions to people, other pets extremely slow allowing cat to dictate pace.
Make Gradual Intros
Use calming pheromone diffusers/sprays or prescription anti-anxiety medication if needed.
Try Calming Aids
Offer treats, playtime and affection when your cat demonstrates desired adjustment behavior.
Reward Bravery