Play follow the leader games with lots of stops and go and give encouragement when the puppy copies your lead.
Keep your head and eyes looking towards, and maneuver your interactions with your puppy to the area by your side close to you. Give praise, naming the behavior.
Make eye contact with your puppy frequently while walking.
Indoors, clip on a light weight leash but leave it dragging on the floor and allow the pup to drag it and become comfortable wearing it. Resist any temptation to tug on it. Instead encourage the pup to walk and follow you.
Provide something for your puppy to look at while its walking with you. Like a toy held on a pole out in front. The dangling "carrot" trick.
Deliver treats next to your leg in the location you want the puppy to walk. Keep walking as you deliver the treat.