Begin training your dog as early as possible. Although old dogs are able to learn new tricks, starting the training early allows for quicker and easier education. What is more, older dogs are going to have more bad habits that you will need to get rid of.
Your dog training should be gentle and humane (after all its not a hunting dog training), and as long as it is possible, teach him by means of positive, motivating techniques. Make obedience sessions optimistic so that the training process is enjoyable both for you and your dog. Some useful positive training methods are presented on this website.
Does your dog make you feel you like “hired help” at home? Does he beg at the table or jump up on your guests? Perhaps ignore your commands? Remember that the quality of your dog’s response to you at home will influence his behavior outdoors. When your dog doesn’t respond properly to commands at home (where distractions are reduced to minimum), he certainly won’t be eager to obey you accordingly outdoors where he will be lured by other dogs, pigeons, passersby, sidewalk food scraps, and many others.
You shouldn’t give your dog commands that you know are impossible to enforce. If you will give a command that is neither complied with nor enforced your dog will soon find out that commands are optional.
Bear in mind that there should be only one response to each command, therefore give your dog only a single command (twice is absolutely maximum!), then gently enforce it. Repeating commands throws your dog out of focus (similarly to nagging) and teaches your dog that the first several commands are a “bluff”. For example, commanding your dog to “sit, sit, sit, sit!”, is not an efficient method to give orders. Just give your dog a simple “Sit” command and gently place or lure your dog into the desired position, next praise or reward the proper behavior. More information about repetitive commands can be found here.
Do not give your dog combined commands which are incompatible. Combined commands, for example “sit-down” will most probably confuse your dog. Following this example, command your dog either to “sit” or “down”. The command “sit-down” is simply incorrect.
When issuing your dog a command, do not use a loud voice. Even if your dog is really independent or unresponsive, the tone of voice when giving commands such as “sit”, “down” or “stay”, should be calm and authoritative, instead of harsh or loud.