Little dogs are often stigmatized as being yappy, difficult, annoying dogs, and while many little dogs do exhibit those types of behaviors, it is not because of their breed or size, but rather, a learned set of behaviors. This is often called "Small Dog Syndrome." Because of their size, little dogs are often allowed to exhibit dominant behavior, since they aren’t as imposing as larger dogs.
The truth of the matter is, however, a small dog doesn't see any difference between themselves and a bigger dog, so even though we see their attempts at being dominant as cute, by allowing this type of behavior to go unchecked, we are tacitly agreeing to the assertion of their dominance.
An easy way to think about how this works is “would a bigger dog be allowed to do that?” If not, than it is probably a problem behavior. If you are afraid that your tiny dog may be headed down the road to Small Dog Syndrome, here are a few things to look out for, and simple ways to break these problem behaviors.
Jumping
If a tiny dog jumps up on your leg, it is often viewed as an adorable display of affection. It isn’t -- a dog jumping up is their way of saying “I own you,” which is no good. While it may seem cute, if you want your dog to be well adjusted, jumping up cannot be allowed.
Same thing goes for climbing up on your lap. If they can just waltz up into your lap whenever they want, they think that they are in charge. You need to make it known that it is you allowing them to be on your lap, otherwise they will start to think they are the alpha, and start to display more dominant behaviors.
Growling
If your Doberman growled at your guest, chances are you would reprimand them, since growling is not appropriate behavior. However, generally when a French Bulldog growls, the guest is simply told to avoid the dog and it is chalked up to moody dog behavior. There is no way that kind of attitude would fly with a bigger dog. If your small dog growls at a guest, you should make it clear that they are not behaving well, just as you would with a larger dog.
Tugging on the Leash
A big part of training any dog to behave is making sure they are safe on the leash, especially for bigger dogs who might otherwise bowl people over. However, just because your Dachshund can't knock you over, doesn’t mean they should be allowed to pull the lead wherever they want. Again, this shows a type of dominance which is only going to strengthen in them the idea that they are in charge. They should never be allowed to pull on the leash. When on walks, you should be in front leading the way, with your dog alongside or slightly behind you. Teaching the heel command is a great way to ensure that walks are an enjoyable experience, and not a contest.
Yapping
Little dogs who view themselves as the leader of the house often become yappy, which is essentially their way of trying to give you commands. Some of these dogs are thought to suffer from separation anxiety, which is a dominance issue all its own, as the leader is not to be left alone. A small dog with separation anxiety typically thinks they are the alpha and is upset about being left by their “followers.” If you make it clear that they are not the dominant force in the house, the incessant yapping should calm down. The "speak" and "quiet" commands are a great way to regain control over your dog's vocalizations, which can also lead to an adjustment in personality.
What You Can Do
If you notice your dog exhibiting these, or other dominant type behaviors, the best course of action is to show them that you are in charge. Consult a canine behaviorist or a dog trainer for help.
Just remember, submissive behavior should never be confused with sadness. Your dog will likely start to carry themselves differently (ears back, head down), but that is because they are no longer challenging you for leadership. It is a good thing.
More on Little Dogs
All About Small Dogs
Small Dog Grooming
How to Train a Small Dog