First, this Instructable is not about how to train a dog, nor is it about what type of collar to use on a dog to prevent bad behavior.
The 'ible is also assuming you are in a situation where you cannot get or do not have a two handle leash where one of the handles is down by the dog's neck. You could tie another loop towards the lower part of the leash to make a 2nd handle. The problem here is the leash will not be adjustable and after a period of the dog pulling on it, the know may be difficult if not impossible to undo.

This Instructable is only about one thing. How to shorten a standard leash, that only has one handle, and still have effective control if the dog starts to pull or is otherwise out of control. Another reason you may need this is if the dog should chew the leash and separate the one handle from the leash.

I don't know how many of you may experience this, but I have been involved in dog rescue for nearly ten years. I mostly deal with larger dogs over 60 lbs and sometimes up to 100lbs. Many of these dogs come out of a shelter untrained with little or no leash experience. As a rescue we use whatever leashes we have and we cannot afford to buy a lot of high-quality double handled leashes.
Besides that, this is just good knowledge to have if you are walking, your otherwise well behaved dog, and come across something they are overly interested in, such as a food court with lots of people eating.

By using this leash holding method, you will be able to hold the dog close to you and gain the leverage of you entire body weight to keep control. Usually people will just wrap the leash around their hand and make a fist to hold it. All the energy of the dog pulling is going to your fingers or, if you are able to grip tight enough, the leash can tighten around your hand and possible break bones or dislocate and break fingers. It happens a lot more then you might think

Step 1: Lay Leash Over Palm of Hand.

Lay the leash over the palm of your hand with the palm facing up. The part of the leash hanging down is called the "excess".

Step 2: Wrap the Slack Around Your Wrist.

Wrap the excess around the bottom of your wrist so it makes a full loop. Make sure you are behind your thumb. This is very important because it will now give you much more leverage to hold the leash.
If you simply wrap the leach around your hand and use your fingers to hold the dog, you will only have the strength of your hand to control the dog.

Step 3: Wrap One More Time With Leach Across the Plam.

Wrap the leash one more time with it coming across your palm. This will help secure the leash. You could probably hold the leash with just your thumb and you will still be able to maintain control of the dog because all the energy of the dog pulling is applied to you hand and transferred to your entire arm and body.

Step 4: Grip Leash Securely

But in actuality, you will want to take full grasp of the leash to prevent slipping.

Now that you have done this, you will be able to hold the dog securely, even if the dog is jumping around and pulling hard. You have the leverage of your entire body and the strength of your entire arm holding the dog. When you hold the leash, make sure the part of the leash that is going to the dog is coming straight out of your grip and not applying pressure to either your forefinger or thumb.

Even a strong 70lb dog can only exert about 100lbs of pull. Even you can't lift 100lbs, your body weight will be enough to keep the dog under control.

This is not a long-term technique to walking crazy dogs. This is a quick fix to get your dog safely through an over stimulating situation. The longest I have ever had to maintain this type of leash control is about 15-20 minutes.