If you are trying to target your lower pecs, position the pulleys at a high position. To target the middle of your pecs, set the pulleys to shoulder height and keep your arms parallel to the the floor, and to target the upper pecs, position the pulleys at a low position. Note: You will need to adjust the weight according to the pulley position. You will be able to use more weight from the high pulley position as opposed to a low pulley position.
Form Tips: Arms are straight, with a slight bend in the elbow, foot stance staggered, core contracted, squeeze the handles towards each other as if you're giving a big bear hug, squeeze the chest at peak contraction and pause 1-2 seconds with each contraction. For shoulder health, keep your arms in your peripheral vision as your arms return to the start position.
I like to do cable crossover ladders: place the pulleys at the lowest point and then do one complete set to failure, then move the pulley position up a notch or two and do another set to failure. Do this until you reach the top position moving up one or two notches each time you reach failure. If you have more steam, ladder back down.