howler said it well,the only thing i do different (besides looking for yucca,don't have any yucca here)is i make my series a little longer.your gonna get alot of different opinons on this,the only thing you can do is find a system that works for you and stick to it.if your system isn't working this year then change,make your call series longer-shorter-louder-softer what ever, and see if something works.when it does work try to remember exactly what you did and repeat it.