Man, is this concept misunderstood by the average runner! But I can see why. When you watch a fast runner, their stride is pretty dang long. Makes sense that you, too, should strive for a long stride, right? It might be logical to ask at this point, “well, what comes first, the chicken or the egg?” Should you work on developing your stride length in hopes of getting faster? Or should you focus on getting faster and just let the stride length do it's thing?
First, understand that under no circumstances should you attempt to increase your stride length just to increase your stride length. Doing this will inevitably result in overstriding. That's the last thing you want.
A long, loping stride is usually considered inefficient because you are crashing down on your heel while it's too far in front of the body and that creates a braking effect. Additionally, you are likely bouncing up and down excessively. Wait. Don't you want to run forward? So why would you want to bounce up and down? That's wasted energy that could be better spent propelling you forward.
Instead, you are better off developing a compact, efficient running stride (try good form here). Your foot should land nearly underneath your body and you will be taking about 28-30 strides every 10 seconds. Anything lower than 28 means you are bobbing up and down too much. Go check yourself right now...
In order to increase stride length properly, you “simply” need to do one thing: run faster while maintaining your great, new form. No problem, right?
Besides lots of running, in order to get faster, one must develop the ability to apply more force to the ground. How to do that? Check out this post. Strength exercises like deadlifts, squats, and lunges will increase the amount of force you can generate. Then once you've done them for awhile and you've seen your strength improve, start adding hopping drills. You need to apply that force rapidly. Simply hopping in place does the trick if you react off the ground as quickly and as high as possible. More on this in another post...
In the meantime, ignore those that tell you to lengthen your stride. They're wrong!