I always try to keep my breathing pattern to 4 strides per inhale and 4 strides per exhale on easy runs. If that starts to get uncomfortable, I slow down slightly. Sometimes I stop paying attention and speed up, resulting in breathing faster, but overall, it works. I eventually realize that it has happened and return to 4 breaths per. It works really really well.
There are many "zones" that you can identify by focusing on breathing patterns. For example, I usually do tempo runs at a pace where alternating between 3 and 2 strides per breath is the most comfortable way to breathe, and steady distance runs are at the edge of 4 breaths per stride, sometimes slipping to 3 breaths per stride.