The first step is to analyze and have a clear picture of how you actually spend your time. People often demonstrate Parkinson's Law that work expands to fill the time available for its completion. One wasted hour each day is equivalent to a six weeks-unpaid holiday. This is particularly relevant if you are doing flexible or unstructured work and you don't have a boss continually looking over your shoulder telling you what to do. I am fortunate to be self-employed, so the best use of my time might be going home to spend time with my family.
Yesterday is a cancelled check, tomorrow is a promissory note, today is ready cash - use it.
Live the moment. Forget yesterday and look forward to tomorrow. If you are guilty about what happened yesterday, or are anxious about what might happen tomorrow, your energy will be dissipated. Plan your work, then work your plan. Reinforce the good daily patterns and break the bad.