Summarize:

” It’s easier to put the harness on the dog if it stands in place. Your dog should be sitting in front of you. If your dog isn’t trained to “sit” and “stay,” you or a partner will need to hold the dog still while you put on the harness. The neck hole should look like a circle that fits over your dog’s head and shoulders. Find the D-ring for the leash, then position it either in the front or the back, depending on where it's supposed to go. Slide the harness over the dog's head and position it low on the dog's shoulder area so it isn't around the neck.  The neck hole is usually the smallest hole on the harness. The side straps will be attached to the neck hole on each side. You want the harness to rest against the dog's body rather than around its neck. If your overhead harness has a vest or comfort shield attached, make sure the outside of the fabric is facing away from your dog. Your harness should have a leg loop on one side. Lift the dog’s paw up off the floor and slide it into the loop. Then, put your dog’s paw down on the floor. If your harness clips in place on both sides, you’ll need to clip the straps around the first leg. Wrap the two straps around the leg, then clip the buckle. This will turn the strap into a leg loop. Make sure the strap goes under and behind the dog’s leg, which is important for control. Once the harness is on your dog, it will look like both legs are inserted into side loops. The strap that you looped behind the dog’s leg will clip into a buckle on the dog’s back. Push both sides of the buckle together, then listen for the “click.” Test the buckle to make sure it’s secure. You should be able to pull up on the buckle without it coming apart. Slide the adjusters to tighten or loosen straps, as necessary. Pull on the straps to check that the neck hole and leg loops aren't loose enough for your dog to get out of them. Then, check that you can put 2 fingers under the straps to ensure it's not too snug. You should adjust the harness every time you use it. Putting on the harness should be a pleasant experience for your dog. This teaches it to like putting on its harness, making it easier to outfit the dog for future walks.
Command your dog to “sit” and “stay. Find the neck hole and slide it over the dog's head. Put one of the dog’s paws into the loop on the harness. Loop the remaining strap under your dog’s leg and up toward its back. Click the buckle on the dog’s back. Fit the harness around your dog using the plastic adjusters. Give your pup a treat and lots of praise.