I like the theory of do what you can, log it, then the next week beat that score. I did that when I started and just kept going up. When I began I could only do 2 pullups without having to rest. Less than a year later I was at level 7 and doing sets of 10 and I'm no athlete by any means.
One thing that helped me also; I added a 20 lbs. vest to the Day 2 after I started improving a lot. I found that D2 was pretty easy and wanted to make it more difficult. The upper levels I had to take it off. I also did two days between of 5 min jog, 1 min sprints, 1 min jog, with sprints/jog of 3 rounds then a 5 min jog cool down. Saturdays I tried to do a long run. That being double whatever the furthest distance I ran on Tuesday or Thursday.
I didn't keep a perfect schedule by any means and made some very good gains.