Save your energy.
In this hectic and fast paced living, people generally tend to get exhausted very easily. The reason for this exhaustion is generally more psychological than physical. The mental tension, stress, anger, jealousy etc. developed out of material greed tends one to impose a lot of pressure on the psyche of the individual. Many generally do not realize that the lack of energy and tiredness is because of such negative emotions, which drain the emotional energy.
The best way to save oneself from complete exhaustion and tiredness is to ensure that such emotional energy drains are saved by avoiding negative emotions. The focus should be on positive emotions, which rejuvenate and keep the energy levels at very high levels. This in turn will make one healthy, vibrant, enthusiastic and mentally strong.
Purity in thought gives positive emotions and thus keeps one energetic.