Used imprpperly collars can do damage to your dog’s neck (including the trachea, esophagus, and more) over the years. An easy way to prevent the damage is to attach your dog’s leash to a harness instead of a collar.
If your dog pulls a lot on his leash, you can buy a training tool such as an Easy Walk Harness or a Gentle Leadeer Head Collar and use that tool on walks while you teach your dog to walk more nicely. (Be sure to follow the instructions when using training tools like these.) Once your dog understands how to walk politely on leash, you can remove the training tool and simply walk your dog in a regular body harness.