Having a well-trained dog on the leash starts with training at a young age. When the pup learns the skill of focusing on you, rather than surging ahead on the leash, then things really start to swing. The best time to start teaching these skills is with a young pup, as his brain is geared to learning and he will pick things up quickly, establishing good habits from a tender age.
However, old-fashioned training methods relied on harsh correction and jerking the puppy roughly on the neck to get him to walk to heel. Happily, these harsh methods are discredited, as teaching through fear and discomfort. Altogether more appropriate methods using rewards are the way ahead.
A well-trained Labrador should walk by your side on a loose leash, without pulling or tugging. Of course, a puppy is easily distracted by a big and exciting world of sounds, scents, and sights, so harsh correction is not appropriate and you should work using reward-based methods to make training exciting.