These are :
These regulative principles are based on the four pillars of religion: Truth (satyam or honesty), Austerity (tapah or self-discipline), cleanliness (saucam or purity), and mercy (daya or compassion).
Truthfulness is the basic principle for all religions.
Satyam, truthfulness, means that facts should be presented as they are, for the benefit of others. Facts should not be misrepresented. (Bhagavad-gita10.4–5)
Satyam. This word means that one should not distort the truth for some personal interest. (Srimad-Bhagavatam 16.1–3 purport)
What are some do's and don'ts associated with truthfulness? Speaking a lie is one way of being dishonest but how else can this principle be broken?
Further reading: Truthfulness, The Last Leg of Religion by Sarvarupa Dasa Goswami
"Without tapasya, or austerity, no human being can get liberation."
Material compassion, lamentation and tears are all signs of ignorance of the real self. Compassion for the eternal soul is self-realization. (Bhagavad-gita 2.1 purport)
Srila Prabhupada defines daya as intolerance of others' unhappiness.
Why is being compassionate and merciful toward other living entities important in spiritual life?
Further reading: Srimad-Bhagavatam 7.9.43, or the story of Mrgari the hunter from Sri Caitanya-caritamrta
In regulated life only can one understand transcendental knowledge. (Srimad-Bhagavatam 3.25.1 purport)
He who is regulated in his habits of eating, sleeping, recreation and work can mitigate all material pains by practicing the yoga system. (Bhagavad-gita 6.17)
A devotee lives a very regulated life. At every time of the day he has something to do for Krishna. On top of that, a devotee needs to know many other rules related to etiquette, cleanliness, and regulation. So many rules and regulations may seem a bit overwhelming at first, but don't worry — we are not the International Society for Rules and Regulations. As long as you remember the basic principles, you'll pick them up and in time they'll become second nature.
What are the advantages and benefits of having a regulated lifestyle?
The Vedic injunctions have a very subtle approach to cleanliness and purity (saucam). For example, they require one to wash his hand after drinking from a glass of water, to not offer food to the Deities if it has been seen by a dog, and to not enter the temple after seeing a dead body. Of course, being externally clean, tidy, and orderly is also included with the term saucam.