Essentially, when you're waiting on a villager to move in, each time you begin your game create a new character (go through them on the train, choosing their house location etc). Then go around town to see where the villager is planning their house. If you like the location-save and then you can set about deleting your new character or using your Mayor. If you don't like the location, quit without saving and repeat the process!
If you start the game when expecting a villager using your Mayor, then it saves automatically, so this is why an extra character is used before you log in for real. However, I stopped using this method myself when I heard a few people got corrupted games from doing it because the game isn't set up for continuously saving and quitting etc. But there are far more people who haven't had any problems, it's your choice! There are also some youtube videos on how to do it too!!