Question on Running Cadence

A) Stride length will give a better increase than cadence.
B) The best answer is to run more.
C) The second best answer is this: Hill Training

Hill training will work stride length or cadence, depending on what you're doing.  This is one of the best ways to improve.  I presonally disagree with using a metronome for the simple fact that you don't know what to set it at, and it creates an artificial cadence that may not be efficient for you. 

I'm no expert - or even a good enough runner to deserve an opinion, but...

First - do you need a higher turnover? The statistic about 199% of elite runners have a turnover rate of blah, blah, blah is only useful if you find yourself in that group of elite runners. IMO

Second - try music. If you grab a podcast like, let's say Podrunner, with a faster tempo that may help. Works for me.

I'm no expert, but increased cadence comes with increased speed.  So just run faster.  LOL

Really, I would just add some strides (short periods of faster running) into your current runs.  About 20 seconds each.  The other thing you could do is cadence drills on your bike (like spin-ups).  Increase cadence on the bike should lead to increase cadence on the run.

Otherwise, you are already following a structured training plan.  Let the speed come to you.

Quick turnover, land with your feet under your center of gravity (not out in front), don't "bounce" up and down, keep "light" feet (don't "pound" or "plod",...

Those are some cues I think help.  Doing strides can also help with emphasizing good form which should help lead to a good cadence for you.  The 'good form' part is probably more important than the actual cadence itself (though working on getting a quicker cadence can often help with some form issues).  90 is often thrown out as a "target" cadence, but people will differ.  But if you are below that level (as you are), it's probably worth working on making sure you are not wasting energy in your stride (braking, bouncing, etc.) that may be leading to a lower than optimal cadence for you.  Don't "chop" your stride just for the sake of getting a higher turnover, but a higher turnover with a shorter stride may end up being more efficient in the long run for you too.

If you do want to use cadence as the focus, you can either run with a metronome or just count strides.

Just to be clear, I don't think you NEED to run on your mid- or forefoot.  However, it can help to think about landing more mid-to-fore as that will tend to force you to land under your center of gravity.  If you reach out in front of this center, you'll likely land heel first and waste energy by "braking" yourself with each stride.

But you can land heel-first while still landing under your center.  There are many elite runners who do so.

OK, foot strike has little to do with improving your cadence.  In fact, it should be the opposite: a higher cadence will shift your footstrike further up to your toes.  But that's a separate discussion.

To improve cadence, you need to improve turnover.  Hills are still going to be one of the best ways to do this naturally.  You don't need a metronome, or anything else, just some nice, gentle downhills.

Can you explain this a little more?  ie how do you increase leg turnover without modifying footstrike? 

Here.

Running a gentle downhill, focusing on a quick turnover.  Footstrike doesn't play into it at all; in other words, you do not, and should not, focus on consciously changing where your foot strikes the ground.  JK is right; over-extending the leg is the problem, not landing on your heel. 

Interesting article.  I still think footstrike factors into the equation mechanically.  You can't isolate the feet from the legs, it's all connected.

I would agree, most people run heel to ball, very few can run ball to heel.  My point was that as you increase turnover, your strike will be less weight on the heel.  Also, a ball to heel strider can increase both stride rate and length, while a heel to ball strider is limited in stride length, and needs to focus more on cadence.  I agree, you shouldn't change your natural stride to the extent that it causes injury, but I do feel this is something that may change slightly as you become faster.