The Baalei Mussar (teachers of ethics) have already written, that if a person would be asked to sell one year of his life, or even one day or one hour, even if he would be offered all the gold and silver in the world, he would refuse the offer. That being the case, a person must ask himself, how can he give away his life for nothing and use it for time-wasting? How can he let his days evaporate like smoke, or use them for enjoyment and light-headedness or forbidden acts, sins and iniquities, to the extent that it were better that he should die than that he should live? Therefore, a man who desires life should be more careful not to waste even a second of his life than he would be careful about a lot of silver and gold, and he should constantly be occupied only with the service of his Creator in thought, speech and acts.
The service of Hashem in thought to fear and love Hashem (who is honored and awesome), and to cleave to Him, and other similar thoughts, is a constant service, and one can perform it at all times, when one is sitting down or walking, when lying down and when standing up. And when a person is busy with his occupation and preoccupied with his employees or engaged in eating and drinking, a man who is good and upright will still not be lacking in this form of service of Hashem. A person who has not the mental fortitude to concentrate on these pure thoughts at all times, should at the very least be constantly repeating and learning things which he knows fluently by heart (for example the portion of the Torah which deals with the Daily Offering, or Shema etc. Other possibilities would include well-known Mishnayos, such as Yehudah Ben Taimo etc. or Rabbi Chananyah Ben Akashyah etc.). He should repeat them even millions of times. Our Chachamim have already said that even if a person spends his whole day repeating the verse “VaAchos Lotan Timna” (Timna was the sister of Lotan.), HaKadosh Baruch Hu gives him a reward in the same way as he would receive a reward for learning the most difficult topics in the Torah. A person is obligated only according to his capabilities. However, whatever he is capable of doing, he is obligated to do and there is no one who can free him from this obligation. And although “there is no righteous man in the land who performs only good deeds and never sins”, nevertheless he must do everything that is in his power, and as regards the rest, “he who comes to purify himself, receives help from above”.