My new puppy also didn't like the leash the first day and is still warming up to it, but the very next day he was walking with me. My little guy and I play a game of chase in the house at times which he loves (he watches me and chases me around lol), so I did that with him on a leash and that got him started.
Once I see him slowing down like he's about to sit I start walking faster or jogging and he quickly follows. If he does sit and doesn't want to budge I pick him up and carry him for a bit then put him back down and start jogging and he follows me. He no longer runs ahead of me...that he seems to have learned on the first day. Everytime he would try to go one way I would start running the other way and go back and forth (changing directions) so he was forced to watch me and move with me. I also try to keep him on one side of me. Just observe your puppy's behavior and try some different things that you think he will enjoy. Maybe carry some treats with you and reward him when he follows you or comes to you.
For what it's worth he's using a collar right now. He has two extra small harnesses, but they are both big on him right now (even the adjustable one
) so he slips his paws through the front part and plays with the harness. I'm not too worried about him wearing a collar at the moment because he's very good when we go walky now and he never tries to pull he just follows me or walks next to me and watches where I'm going. So he doesn't pull and I don't tug - don't think the collar is doing any damage in this case. I will try the harness though once he grows into it and see how that affects his walking behavior if it does. Good luck with your puppy!
Desiree & Eros