I would imagine you want to keep it light almost like face pulls, band pull aparts, etc. The point is to strengthen all your scapula stabilization muscles (all the muscles that move the scapula in every direction it's capable of). If it gets easy then add weight but don't worry too much about how much weight is being used - you have to start from somewhere. You should feel all the muscles attached to your scapula being used - upper, mid and lower traps, rhomboids, levator scapulae and serratus anterior. Focus on a large range of motion to hit all involved muscles.
Edit: Look up where those muscles are located to have an idea of what is being targeted. Also, keep your entire upper body tight while doing the sets.