Dogs hate the leash. If they can have their way, they would rather not be restrained. This is especially more so if the dog is one from among the active type of breed. This is why a dog has to be trained to get used to the leash as early as possible. The following are tips to ease the dog in getting used to the leash.
The first time is typically the hardest. When attaching a leash for the first time, try attaching the leash hen the pup is at his best mood. Better yet, attach the leash while the pup is eating. The idea is to attach the leash the first time associating it with happy occasion or at least occasions that are non- threatening. As much as possible, the leash must never be attached to the dog in ways that will be interpreted as punishment, at least not during the first few times.
Initially, the pup will jump, pull, nip, whine, and show fear when leashed. There are plenty of good reasons for this. But aside from its natural tendency to refuse restraints, the first experience with the leash must not have been pleasant. Check whether the leash is too heavy for the pup, and check if the collar is too tight. Being leashed is not pleasant for any creature. The best thing to do is to at least make the leash very comfortable. That one resolved it is now time to take the pup for short walks around the yard.
Attach the leash to the pup and encourage him to walk on his own. Do not hold the leash yet. Encourage the pup to come to you and when it does, give the pup treats. The idea is to get the pup get used to the idea of walking with a leash. Do this for a few days until the pup is used to walking with the leash.
After a few days the pup will appear comfortable already, hold the leash for short periods of time, but let the pup guide the way. Go with his phase. Do not pull at the leash yet, during this initial stage, it is best to give the pup his space. Remember that you are still inside the home or within the confines of your yard. This is already control. If the pup insists on going to places where you do not want him to (like digging on a flowerbed for example) and you are tempted to tug at the leash, carry the pup instead, then move to another location.
You could already take a more firm control when the pup appears to be comfortable being restrained. Tug gently at the leash when he wanders to places that are not good for him. Be gentle when doing so to minimize the threat as much as possible.
Eventually the pup will not mind being restrained. If in your judgment the time is good, that would be the time to take the pup out. Then it will be a real walk in the park.