The proper lead can make a difference for you and your dog. I like a leather lead, and it should be a comfortable width in your hand, but still not so large that it will weigh down a small breed. I use a chain collar, because the noise the chain makes and not the tightening gets the message to the dog well. Some use a leather or fabric collar, but generally an attentive dog is most likely to be successful being trained on this collar. A dog that pulls likely won't train well on a leather or fabric collar.
Many new handlers pull, rather than quickly correct and then release the collar.
Pulling makes the dog resist and pull in the opposite direction. Initial heeling can be done in a circle to the left, because this keeps the dog closer to the handler. A dog that pulls a lot, and needs a lot of correction can often be trained successfully by taking a lot of turns with just a few steps in between with a leash snap and praise on every corner. The multiple turns help the dog be more attentive to you. The proper heel position is with the dog's neck and shoulders even with your left knee.