One good way to add miles to a training program while minimizing the stress is to add two easy runs on the same day. I live 5.7 miles from Hillview so if I run to and from work I get at least 11 miles in. If I run with my kids I get even more miles. Not wanting to over do it, I stuck just to the run to and from Hillview. My run in was 5.7 and I took a slightly different route home which is exactly 6 miles. I always seem to struggle more in the morning than the evening – both ways I took it easy: 9:10 pace to school and 8:50 coming home (into a consistent headwind most of the way)