Teach Your Dog "No"

"No" is one of the first and most important commands to teach your dog.  When you need to use this command, you should only use it once.  If you say, "Spot, no. No. Quit it right now. No!" your dog will learn that you don't really mean no when you say "no".  Obviously, you don't want them to think that.  

However, you don't want to overdo it either so save it for when you need it.  For example, if you are teaching your dog a more complicated command and he isn't understanding it, don't use a harsh "No", simply start over again.  The best time to use this command is when your dog is doing something overtly wrong like getting in the garbage or climbing on the furniture.  A curt "no" as you refocus your dog's attention should do the trick.