Once inside, your immediate goal is to locate the Red Key, which unlocks the door to the basement. The Red Key is typically found on the second floor, often in the Neighbor's bedroom or a nearby bathroom. To reach the second floor, you'll need to navigate the main staircase. Be wary of the Neighbor's patrols; he frequently checks the stairs and main hallways.
Before heading upstairs, consider disabling any security cameras or traps you encounter. Some doors might be boarded up, requiring a crowbar (often found in the garage or shed) to remove the planks. Once on the second floor, search thoroughly. The Red Key is a small, distinct object. It might be on a nightstand, a shelf, or even hidden under a pillow. Once you have it, proceed cautiously back to the basement door, usually located on the ground floor or in a utility room. The Neighbor will be actively trying to catch you, so plan your route carefully.