In breaststroke, timing is everything, and knowing when to initiate the kick is a critical element in that timing.  Steve Haufler's Separation Drill does a great job in over-teaching this simple step to a great breaststroke.    On Steve's DVD Go Swim Teaching Progressions, you'll see how effective this drill is for teaching breaststroke to the under-10 age group.  In this drill, you'll see that it works equally well for Masters swimmers.  

Why Do It:
The later you initiate your kick in breaststroke, the less likely you are to create unnecessary resistance with the recovery of the kick.

How to Do It:
1.  Start by totally separating the pull and the kick in breaststroke.  Pull with your legs held together through the entire phase of the pull, until the arms are completely back out front, and the body is sinking back into the water, with the head between the shoulders.  
2.  Only after you've gone back to the streamline position, do you initiate the kick.  Each move is completely separate.  Remember, think of this as a drill; don't try to swim breaststroke.  First you pull... then you kick.
3.  Now have less separation between the two, making sure you keep your feet together through most of the pull, allowing the action of the pull to draw the torso, hips, then thighs up into the recovery of the kick.  Reach full recovery with your hands long before the kick is initiated.
4.  Finally, merge these two moves together a bit more closely.  Again, make sure the pull has completely finished out front prior to initiating the kick.  

How to Do It Really Well (the Fine Points):
The trick to this is fighting instinct.  Treat it as two drills: a pull drill, then a kick drill.  Then slowly merge them together.  It helps to keep the feet together, with toes pointed, during the pull.  This keeps the legs long, and helps to avoid an early draw of the feet.