Here are some things I might do:
Do only one step heeling.
Do one step heeling facing a wall leaving yourself only one step plus a tiny bit. Praise proper sits BIG BIG BIG time.
Teach the dog to move in towards you, out away from you, up towards you, and back towards you, on verbal commands. I use the commands Get In, Get Off, Get Up, and Get Back for this. Once the dog learns these, play lots of finding heel games.
Work for very short bursts, and then break for praise and play. One or two reps, toss the toy, feed the treat, play tug, etc.
Teach fronts, and play the No Lookie No Cookie game. When they get onto this, shape real focus in heel position.
I have also used a small dowel held across my body so that if the dog forges it touches the dowel.
Teach the dog to heel backwards and sideways.