One of the most common problems with owning a dog is that all that good behavior goes out the door when new people come into the house. Dogs have various problem ranging from overexcitement to aggressive tendencies when it comes to visitors in the house.
Here are some tips on how to help your dog overcome their problems with strangers in the house:
1) Practice everything that excites your dog with no guests. For example, if your dog goes nuts when they hear the doorbell or a knock on the door, you have no chance when there is actually somebody on the other side of the door. Make sure you desensitize your dog to these usual triggers and also use them to indicate a beginning of an obedience routine. Meaning, ring the doorbell and send your dog to their place and reward thoroughly. If you practice this, then the doorbell will mean "go to your place" rather than "attack the door."
2) If your dog is uncomfortable with people, food is the easiest way to right the ship. I like to teach people that when guests come over, the dog should be given treats by each guest. It's important to start this as early as possible. There should also be a hierarchy of treats that your guests give: Women should give something low value, but enjoyable like kibble. Men should give something higher value like a good treat or peanut butter. Kids should give the highest value treat imaginable. The more consistently this is done from the beginning, the less problems your dogs will have with guests.
Note that if your dog has already begun biting or is under extreme anxiety, this is much more difficult and may require the help of a professional.
4) Don't lose control of the situation. If your dog needs to be on a leash to stay out of trouble and to have a clear routine, then that is how you should do it. If your dog is under stress, bring them to the guests just for the treats and then take them away from the situation.
5) Try taking a walk with your guest and your dog. Dogs make friends quickest by walking together - whether that is with other humans or other dogs. It is also something high value that they will come to associate with strangers! If you do this regularly, your dog will view strangers coming over the same they view you when you pick up a leash - a sign of great things to come.
6) Get everyone involved. Use this opportunity to reconnect with people in your life and invite them over to help. Getting yourself social is a great way to improve your dog's socialization. If they don't have any practice, they aren't going to get any better. You probably have spent your life building up a list of facebook friends, it's time to start using it for good.
7) If you're not making progress or it is getting worse, contact a professional right away. Even if your dog does not exhibit aggression today, unchecked issues with strangers can escalate quickly if a dog feels repeatedly threatened by your friends and family!