To call coyotes, the prime time is moonlit night, at dawn or dusk. Although you can call coyotes during the day time, you will find it very difficult to find and keep their track.
Try to stay far from the road, as it is only a matter of luck that you find a coyote near the road. They are killed by the fast moving vehicles or become road shy. This is the reason they stay far away from the roads.
The rate of success depends on area to area. For example, sometimes you can have one success in eight sets while at other times more than one. So be realistic and do not panic in a few sets.
Do not worry about which call you use to lure the animal. Almost all calls in the market are effective predators but as said the success depends on many other factors than calling itself.
Also, do not worry about tunes on the calls. There is no specific one tune that is more successful than others. You can make dozens of different tunes on the calls, and almost all of them are effective in calling coyotes.
Setting up calls is the most critical part of the calls, so make sure you do not let the coyotes suspect the trap. They can smell and even see you setting up calls and can get far away.
Before setting up a call, try to find something to offer yourself a cover. It can be a tree, a bus or a hay bale. Make sure you do not let the animal see your movements as it can suspect the trap and might not turn up.