And keeping the tough days tough!
In training you want to keep hard days hard and aerobic/easy days aerobic and easy. If you have strength training on your plan for the day, that is hard. Keep the day hard by adding in a second workout, like a tough hill hike if you are not running or do a run with hill strides or short intervals. Then the next day can be an easy day which means recovery and coming back feeling better than before the workout. An easy day can be a 45 minute aerobic run, an hour easy spin on the bike trainer or a row with some corrective exercises with body weight only.
"Slow, easy running helps to flush oxygen-rich blood through the legs and also heals micro-tears and other damage that a workout creates. As soon as you begin to push the pace, you are creating more damage to your legs rather than helping them heal."
Think back on your last few runs. Were those runs easy or hard? If you are unsure, it is time to go out with purpose and know the goal of the run and the effort it will require.