Always include exercise and relaxation. This is not wasting time, this is detrimental to productivity. Give yourself at least 10 minutes at the end of each day to evaluate what you accomplished, carry over the items you did not complete, cross off the ones that can be trashed and get some rest. Guilt is not acceptable. As you approach tasks, focus on one at a time and see it through.
Many people do a little here and a little there and in the end, nothing is accomplished.
The exception to this approach is when you are doing difficult long range tasks. The body responds to stress by activating the fight or flight mechanism. Response to stress may include increased heart rate, blood pressure, blood flow to muscles and brain. The body may experience increased glucose levels, oxygen consumption, and strength. If the body can not respond by fighting or fleeing, the muscles tense up and tighten.