Heavier cover and if you are concealed well, you can call almost continuously. For more open ground the above advice is good.
I never keep calling if an animal is coming towards me. If they stop for more than 5 seconds I give a lip squeek, more than 30 I give a real light distress call. If they sit down, you probably won't get them to stand back up so get ready for a shot. A very experienced coyote hunter told me that when a coyote sits down it is to help steady their gaze, much like when we put our binocs on our knees to steady them. When they do that they were alerted to something, a flash off your gun barrel, a small movement, etc. I don't know if his theory is true or not, but it makes sense.