Only have had my 13 week old puppy less than a week, and he's already walking pretty well on a loose lead with only occasional resistance. The key to not have a pulling dog (learned from stubborn AmStaff) is not to engage in pulling. I use the dressage concept of "half halt" with a small correction upward, not a tug forward or back, followed by moving purposefully in the direction I want to go. No treats on walkies, since I don't want him stiffing around for food when he's supposed to be paying attention to me. Short practice sessions of only 5-10 minutes is all his brain can handle right now, and we follow it with serious play time. I use a martingale collar because it gives an effective gentle upward correction then loosens immediately after. Lots of verbal praise & pats/scritches too. He really prances when he gets it!
In dressage riding, a half halt is a quick closed hand accompanying a closed leg. The leg encourages forward, the hand says "listen, this is important" and converts impulsion to a more collected energy.
Corrections must be subtle but firm and timed well so they're more of a nudge to distract from whatever is causing him to pull, and moving with a happy "Thabo, heel" or "Thabo, come along" seems to do the trick.