Strides - short repeats at a 5K pace with recovery in-between. Each 'repeat/stride' should be about 20-30 seconds long and allow for a full recovery in between. Make sure you are properly warmed up-at least 10 minutes before the first. You are looking to get in about 45 left OR right foot strikes per 30". Multiply by 'two' for your RPM. So 45 left foot strikes per 30 seconds will equal 90 RPM, a running cadence that is the most efficient. You will typically be doing 4-10 repeats of 20-30" strides with a full recovery between sets (depending on the particular workout) by walking back to the starting point.
Over time with these workouts, you will see your cadence quicken, you will be lighter on your feet, and your run times will improve.