One of the best books I've ever read is Flow-The Psychology of Optimal Experience by Mihaly Csikszentmihalyi. This book has pretty much ZERO to do with running, but nevertheless there is a connection that can be drawn between Flow and running.
What Flow posits (in a nutshell) is that what ultimately turns people on more than anything else is a state of consciousness referred to as 'flow'. 'Flow' can be described as a state of concentration so focused that it amounts to absolute absorption in an activity.
I read Flow years ago, but I immediately made a connection between the idea of 'flow' and 'the runner's high'. I've had MANY times during my running in which I truly become absorbed in the act of running and all of my energies/attention are consumed with the act of putting one foot in front of the other.
Since the age of 15, I have always hit the road (whether for a training run or a race) in search of 'flow'. The good news is that I often can find 'flow'. Sometimes I feel it as soon as my foot hits the ground. Other times, I don't really find my flow until I am halfway through my run.
Unfortunately, there are some days in which there simply is no flow to be had. Maybe I didn't sleep well the night before, maybe I'm stressed, maybe I need more time to recover, etc. But, I always have faith that the 'flow' will come another day and sooner rather than later it usually does.
For those who have never experienced 'the runner's high' (or 'flow' as Csikszenthmihalyi calls it), there are a few things I'd encourage you to do to help 'facilitate flow'-
1)UNPLUG/SIMPLIFY. Seriously, if you're strapping on your Ipod/MP3 for EVERY single run you do, you're missing A LOT while you're out on the road. I'm not claiming I don't do it, but part of becoming a good (or great) runner is really dialing into the messages your body is sending you. CONSTANTLY listening to music to effectively 'distract' yourself from the act may very well keep you distracted from messages you should be listening to and keep you from achieving 'flow'. I would also say being overly reliant on heart rate monitors, watches, and GPS devices can potentially make it more difficult to achieve flow. I'm not saying don't use them, but don't OBSESS over them.
2)LISTEN. Let's assume for the sake of argument you elect to unplug your MP3/Ipod and hit the road. The act of running is DEMANDING and taxes your body in a way few other activities do. Fortunately, our bodies do an amazing job of providing feedback, but you have to pay attention and listen closely. Is something feeling tight or fatigued? Are you breathing heavier than you normally would? Are you feeling sharper/fresher than you have for the past few runs? All of this is INVALUABLE data that you should be paying attention to.
3)RESPOND ACCORDINGLY. So, let's assume you're pretty dialed in to what's going on internally. Let's further assume you're feeling sharp/spry. This may very well be a sign that your body is ready to take on more. Perhaps this means more mileage or a faster pace. It's possible it means both. Conversely, you may just not be feeling sharp for a run that might ordinarily be easy. This likely means you need to run shorter and/or dial back your pacing. Whatever message(s) you're receiving, 'go with the flow'.
The ability to go with the flow when it comes to your running is invaluable. We are very fortunate to live in a day/age where we can rely on external tools like heart rate monitors, GPS devices, etc. to help structure our training and guide us towards achieving our running related goals.
BUT, these external tools are not the end all/be all. Don't ignore your gut and don't ignore the messages your body sends you at the expense of whatever 'target training zone/pace' or 'mileage goals' you might have.
Look at some of the best runners on the planet coming from the Rift Valley in Kenya. Most (if not all) of them run in minimal shoes (if they're even wearing shoes). They typically don't have heart rate monitors, GPS devices, MP3 players, or even watches.
So, how is it that they have become such remarkably talented runners? There are a myriad of answers to this question, but a BIG one is their ability to 'intuit' what their body can handle on a given day and 'go with the flow'. This may mean dialing it back or dialing it UP, but these runners ALWAYS listen to their body and ultimately, this is the best tool one can use in determining what you can handle.
Next time you go for a run, try NOT wearing a watch. Or if the idea of not wearing a watch doesn't work for you, try not looking at your watch. Try not to think too much about your pacing and simply listen and respond accordingly to the messages your body is sending.
I can promise you that this approach will get you closer to 'the runner's high' and/or 'flow' pretty much anytime you hit the road. Independent of any specific running goals you may have, don't lose sight of enjoying the act itself which is really what flow is all about.