Here's what I do. Remove the cable from the derailleur. Adjust the low stop screw so the cage just contacts the chain. Yep , you want it to touch. Now put the cable on the derailleur pinch bolt, pull on the cable moderately hard while tightening. Once the pinch bolt is tightened. Back off the low stop screw, the spring tension will pull the derailleur away from the chain and take the slack out of the cable.