Lars,
What part of the country are you hunting? Out west there is very little cover for the coyotes and you can see them at greater distances. In the east where I live, there is a lot of cover and they use it to check you out. Patience is the name of the game. You want to call enough to bring the coyote in but not enough that he finds where you are hiding. I call for 30 seconds and then wait 10 minutes just scanning.
I practice my calling on the back porch and even though I don't think I sound like a dying rabbit, I have consistantly called in dogs, cats, possums and coons. I called in a coyote once that snatched a live rabbit out of the yard not 10 feet from me. That really startled me because I didn't know he was there until he hit the rabbit.
Find what works in your area and good luck, I love this sport!
QAZ