Apollo (formerly Sky King) first day on leash...

This spectacular guy is now a member of T's family...here he is learning to lead. Everyone has their method/s for leash work etc...mine are quite simple, as these are Collies.
Collies are born knowing almost everything.

I don't involve myself with the puppy when he/she have just been set-up in a leash for the first few times. They will mostly scratch their necks in an attempt to remove the lightweight slip-lead that I use (attached to my personal Schutzhund leash which wraps around my body for hands-free work). I have yet to meet a Collie who wants to resist/pull. If they do, absolutely give them more leash, do not ever pull on the leash. Because, they  resist similarly to you & I...& I posit this interesting experiment:

Pull on someone's shirt, grab them close to their neck, perhaps by the shoulder...they'll be offended (that's certain)...they will resist most likely...& finally, they may counter-offend...

Apollo did what most puppies...he rolled around with the leash, bit the leash, wrapped himself up in the leash & then followed me like a champ. The total elapsed time of these sessions should never exceed 5 minutes, should never chaotic, distracted or negative, should never involve other dogs or multiple people & should always be positive.

As for collars, we send our puppies home with a martingale collar...we NEVER leave collars on our dogs. In my opinion, doing so invites trauma & tragedy such as strangulation. Dogs can get hung up on almost anything from brake pads, crates, bed frames you name it...

Regarding leashes, our puppies go home with a very long leash, as we desire for them to have as much initial freedom on the leash as possible...they will learn to follow you because they love you! Not because they are forced to follow.

I consider leash work to be very similar to equine dressage...your hand should be soft, your fingers should gently convey messages & your role should that of a partner.