I started running again in fall 2013 after a long lull of ten years. I was never a good runner, and I found not only was my natural talent lacking, but my form was, too. I watched a bunch of YouTube videos on it and gave it another go. It turns out having good form took care of my joint pain.
About two months ago I bought a Garmin fitness watch. It included a heart rate monitor. I partly justified this thinking about my mountain snowshoe hikes; when I pause I can hear my heart going "tickticktick." I figured monitoring it could be interesting and helpful. But as long as I was running, I'd use it there, too.
Right off the bat, my heart rate was much too high. The normal calculation people do is Max HR = 220 - age. This gives 185 for me. Then they shoot for running with their heart rate around 80% of their Max HR. I was constantly in the 180s and even over 190 when I was running my typical 2-4 mile runs.
So I made a point of running slower. I gave myself a 180 bpm heart rate maximum. This is still too high, but I had to start somewhere. My watch alarms if I hit 180, telling me to slow down (or sometimes me telling it to shut up as I'm almost up this hill).
I've also started doing interval runs. These are supposed to help strengthen your cardiovascular system, and a stronger system needs to pump less often.
Today I looked for similar runs to compare. I have two roughly two mile runs in the flat subdivision where I live.
February 27 I ran 2.15 miles averaging 9.00 min/mi with an average HR of 168 bpm and max HR of 188 bpm.
March 17 I ran 2.06 miles averaging 8:49 min/mi with an average HR of 162 bpm and max HR of 176 bpm.
So my conclusion, and why I felt it was worth sharing, is I think paying attention to my heart rate has helped. These times are still slower than if I just give it all; I could come in under 8:00 min/mi on this route. But I do think I'll keep making speed gains and will definitely be making distance gains. This feels as important as those YouTube videos a couple years ago. It feels like learning to run all over again and coming out at the end enjoying it so much more. Unexpectedly, running seems to be morphing from something I do to stay fit to something I enjoy for itself.
The heart rate monitor helped me, but just the observation of where my body starts to say "we can't keep this up" has helped me. My watch doesn't yell at me much anymore, and I'm probably going to lower the alarm threshold.
I went out running two to three times a week for something like seven months with a HRM before switching to another sport. I usually have problems with sticking to a habit like that, and I can attribute my unusual diligence almost entirely on the HRM and data-tracking with Endomondo. Having multiple metrics to judge my run by instead of just 'it went okay' definitely motivated me. Does your watch also track calories per run? I found that to be a good measure of effort, especially with a HRM. Speeds can vary but I always tried to keep the calorie trend upwards.
When it comes to your ideal running speed and heart rate, I used a treadmill to figure out what's best for me. My completely unscientific measure was that I should be able to sustain 10 minutes at that speed and not be completely out of breath.