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.