For anyone browsing Malachain, here is a clear starting point on the subject.
A rescue dog arrives tired, unsure and in need of quiet far more than excitement. Before the first day, set up a bed in a calm corner, agree the house rules with everyone, put away anything chewable and plan the first week with no visitors. Let the dog explore at its own pace and keep the first walks short and close to home.
The common advice is three days to decompress, three weeks to learn the routine and three months to feel at home, and it is broadly right. Feed at the same times, use the same words for the same things, and reward calm behaviour rather than correcting nervous behaviour. Patience in the first month is repaid many times over in the years that follow.
It also helps to talk the subject through with friends or colleagues who have tried something similar. Their experience points out the details that guides leave out: how long things really take, which costs were unexpected, and which shortcuts turned out to be a mistake.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.