If your dog has been inactive and not exercised on a daily basis starting a regular dog walk has to be gradual. First time you take your dog out, go for a leisurely 20 minute walk. During the walk evaluate your dog – could he have gone for a longer walk or was the walk a challenge? If he could've done with a bit more, next day add another 5 or 10 minutes to the walk. If it was a challenge go for 20 minutes only again, until such time that you feel your dog can do with some extra time.
Over the next several weeks you will notice your dog’s (and your own) stamina will increase and you will be able to walk for longer periods of time and at a faster pace. Your dog will be grateful and you, yourself will be in better shape.
When it comes to the daily walk consistency is the key. If you think that the demands of your career, family, or commuting will stop you from properly exercising your dog, or if you are physically unavailable to take your dog out for regular walks, consider hiring a dog walker to fill in for you.