As far as lead training goes, I found that at about 16 weeks, Xanthe began to seriously forge. This after 8 previous weeks of no problems at all on the lead. It simply started one day, and no amount of patience, commands or rewards seemed to curtail the behaviour. Our vet recommended what's called an easy walk harness. Rather than a nose piece, this one clips the lead onto the breast, which nudges a forging pup toward you and softly impedes her shoulder movement.
Literally within minutes, Xanthe was back to her previous pattern of heeling, with no discomfort. After about a week, we introduced her to a long lead (a reel type) which she was able to use with little to no problem with tugging.
Every so often we go back for a walk with easy lead as a sort of intermittant reinforcement
It looks like this