HOW OFTEN TO WALK YOUR DOG

As an adult dog then no matter what breed you have your dog absolutely requires a bare minimum of 20 mins a day off lead exerting exercise, if you provide less than this but expect a dog with good manners then you need to rethink your expectations. This does mean you need to always find and area outside of the home to allow your dog off lead half the week this can be at home in the garden using games of fetch or with the flirt pole etc, however your dog should be still getting a walk outside the house on these days even if just for 10 minutes around the block on lead. It is vital your dog is frequently allowed off lead to play, run, sniff and explore, without this natural behaviour and stimulation you are going to create a frustrated dog who wont focus, wont interact well with dogs or possibly people and will not have good recall when they are given freedom.
If your dog has poor recall or is reactive with dogs or people give them their free roaming time on a long line where they cant escape . When using a long line in this way it is vital you are still using a short lead for on lead walking, when you want to give the dog free to roam time unclip the short and clip the long all at once (so the dog doesnt notice the long line being attached but does notice short lead removed, this will help in future when you want to stop using the long line the dog wont know he cant ignore recall or run away). Extendable leads are of absolutely no use unless you are wanting a dog that will always pull on the lead as they will learn the sometimes they pull and go further, you can you them in the same manner as a long line so the dog knows when s/he can roam or not, alternativly you can also teach a command for when the lead is short and release command for when the dog may roam. 
Puppies are different particularly so in large dogs, there bones and joints are still forming and so you must be careful not to over exercise. On a daily basis follow these guides for how long to walk your dogs , toy to small (think size of a springer spaniel as max size) dogs should have two walks of 10 mins per month of age a day. Meduim to large (dogs that will get upto the size of a doberman max)two walks of 5 minutes per month of age a day. Gaint breeds such as great danes and Neapolitan mastiff 5 mins per two months of age. The occasional longer walk would be ok but do not do this frequently even if it makes a puppy easier to deal with. Stick to these rules for 12 months, 18 months for the giant breeds. Puppies after vaccination  need to be outside the home every day it is vital they are learning different environments at this age, I also recommend letting young puppys off lead right away whilst they are too scared to wonder they will learn manners off lead and be far less likely to bolt in future, absolutely do not wait for a puppy to mature to let them off