What it looks like: Your dog comes to attention and sits directly at your side.
With your dog on leash (if needed) walking towards you have treats in your right hand, extend your hand towards your dog and lure your dog by your side and as your dog passes your leg, step back with your right leg, lure your dog into doing a u-turn (so that you and your dog are facing the same way)bring your right leg back next to your left leg, click and reward when your dog is right by your side.
Keep doing this until your dog begins to anticipate making that u-turn.
Next when your dog is by your side at the end of the trick instead of clicking bring your hand upwards to lure into a sit. When your dogs butt touches the ground click and reward. Keep doing this step until the dog no longer needs to be lured into a sit but starts offering the sit.
Next work on fading out the step slowly. take a 1/2 step back then a 1/4 etc.
When you no longer need to take a step back move on to the next step.
Remove the treats from your hand, still making a fist to have the illusion that there are treats in your hand.
Next would be to have a open palm to lure them, still clicking and rewarding when your dog sits next to you.
Finally start phasing out your hand cue. instead of extending your hand in front only put it out 75% then 50% until you no longer need to put it in front of you and still lure the dog back and u-turn then sit.
Then begin the phase of luring behind you a little bit at a time. Once you only need to slightly lure the dog begin to add the verbal. Say Finish when your dog is in front of you and you only really need to put your hand a little bit behind your body then by your side. Eventually you will only need to say the verbal and the have your hand by your side. Eventually phasing out the hand cue.