Circle of Fourths

Practicing a circle of fourths is great for ear-training and for remembering flatted sevenths. On your bluegrass stringed instrument of choice, sound out a C7 chord like this: C E G Bb. Notice the tension in the Bb note and how it wants to resolve to the A note which is the color tone of the Four chord: F A C. Now form an F7 chord: F A C Eb and notice how the Eb wants to resolve to the D note which is the color tone of the Bb chord. Here are the chords in the circle of fourths:
C E G Bb; F A C Eb; Bb D F Ab; Eb G Bb Db; Ab C Eb Gb; Db F Ab Cb (enharmonically the same as a "B" note); Now switch to sharps instead of flats to make it easier: F# A# C# E; B D# F# A; E G# B D; A C# E G; D F# A C; G B D F; and now you're back to the C chord.
Try this exercise over and over until it becomes second nature to hear these tensions and resolutions.