with him or her on leash if s/he goes to the end of the leash, change direction and keep walking at a quick pace.
when s/he comes near you on the side you want her or him to walk, use a cheerful voice to praise. whenever s/he gets into heel position or puts slack in the leash, say yes and treat. also, reward for any eye contact.
if after a couple minutes you don’t find your dog spending more time at your side or with a slack leash, consider moving to a less distracting area.
you may also reward more frequently, delivering the treat in the position you want. the point in doing 