Watch the Call And Response online guitar lesson by Jeff McErlain from Blues Survival Guide: Rhythm Edition
The call and response blues form is a classic. Here we are taking the idea that a singer will be singing over the first two bars of each four bar phrase of the blues, we call this the call. The response is on the following two bars, this is the musical answer to the musical question just asked. This is exceptionally common, if we listen to Hendrix's Red House we can clearly see this demonstrated. The key here is to make sure we stay in time and in the phrase length of 2 bars. If we start end too soon or late, or if we come in too early or late the fill will sound wrong or off. This is one of my favorite things to practice.