Once you locate just stick with the one call this time of year. Cottontail should be great.
Biggest mistake new callers make is being too loud and too long winded at the beginning of the sequence. Start off very small and timid. Think
"I'm in distress, but not yet being torn apart." Convey that in the temperament of your call. Remember you are talking to the coyote through emotion.
Cottontails have very small lungs. Be sure to represent that in each blast.
No coyote is going to mess with a 300# rabbit so don't sound like one 
After about 10 minutes of calling start to increase both volume and excitement. Thinking like the rabbit you are now in
extreme distress. I like to imagine I am being ripped apart by a small fox or martin. Something that is not big enough to kill me right away. Make that coyote think he can come steal some easy vittles from a smaller predator. Again, don't forget you are a small rabbit with small lungs - loud does not mean long drawn out blasts.
Have you ever seen a small dog like a Yorkie trying to kill a toy? They pin it down, bite it, shake it, flip it and repeat. Try to imagine yourself being that toy and transfer that emotion and distress through the call. This I will do for an additional 5 to 10 minutes.
After the extreme distress series of calling you want to once again reduce volume and enter the
exhaustion stage. Here I imagine that I am now just minutes from death having no more energy to fight off the small predator. My face often falls deep into the dirt and I moan with every small breath I can muster as the fox or martin begins to eat me alive. This is not a stage of distress or blasting. Just slow moans of exhaustion and life escaping form my little rabbit body. I do not call constantly at this time. This final sequence is no longer than five minutes.
If after these three sequences I have been unable to bring the coyotes in I sit still for another 5 to 10 minutes before picking up and moving location.
I can not express the importance of imagination here. You don't ever want your quarry to ever think you might be a human blowing on a call. And you never want that coyote to think you are too dang big to be an easy meal. Imagine yourself as that poor little flea bitten rabbit - little, fragile, scared to death, and slowly dying at the hands of a predator only slightly larger than you are. This is where a digital caller can never compete with a good hand caller.
If you can visualize that and portray that image through your call you are going to kill a lot of dogs
