Howler,
In time, hopefully you'll get to see one work all the way in. In any event, I watch body english all the way. It's been my experience that on a relatively calm day, a responding coyote knows exactly where you're at from the get-go. Generally speaking, he'll work his way toward you and it's at this time, I observe and am prepared for whatever might happen. If he's coming in hard and it's not especially cold out, I suspect he's got competition on his tail. Along that vein, he may occasionally look back or in one general direction as he approaches. If he zigs and zags as he responds, make sure that there's a reason such as topography or brush to force anything but a straight-on assault If he's cutting a wide arc, he probably has been there-done that before and is antsy.
On a calm day, most of my coyotes come in head down, loping along casually. There's generally no stopping along the way and raising his head up high to look around unless he's been given a reason to do so. Conversely, on a windy day, the coyote is unable to pinpoint your position, so he may be looking all around as he approaches. It's not that he's suspiscious - he just can't pinpoint you with hearing alone, so he's looking for visual indicators such as movement, etc. All in all, just make sure you're comfortable before you start blowing. Make sure your approach is as queit and concealed as possible. Once you start calling, sit perfectly still and let your camo work for you. When you spot an approaching coyote, shut up. Only offer more sound if the coyote is obviously unaware or uncertain of where you are and needs some coaxing or redirecting. And even then, keep it short as in a kiss or mousesqueak. I'll even cover my mouth and try to direct the sound anywhere but straight out front. If done right, it's not unusual to have a coyote walk right up to you and look "through" you for his dinner. Do that one time and I guarantee you'll be addicted to calling for the rest of your life!
