There is already a discussion on ethics and morality in a related question, 'What are the canonical texts in Hinduism for morality and ethics?'. Here are some additional teachings.
Bhishma’s morality
Bhishma said, ‘Knowing how painful it is to himself, a person should
never do that to others which he dislikes when done to him by others.’
Mahabharata Santi Parva Section CCLX
Protest against slavery
Tuladhara said, ‘…Men are seen to own men as slaves, and by beating,
by binding, and by otherwise subjecting them to restraints, cause them
to labour day and night. These people are not ignorant of pain that
results from beating and fastening in chains. In every creature that
is endued with the five senses live all the deities, Surya,
Chandramas, the god of wind, Brahman, Prana, Kratu, and Yama (these
dwell in living creatures). There are men that live by trafficking in
living creatures!
Mahabharata Santi Parva Section CCLXII
Treatment of servants
Bhishma said, ‘…One should not make distinction between one’s guests
and attendants and kinsmen in matters of food. Equality (in this
respect) with servants is applauded.’
Mahabharata Santi Parva Section CXCIII
Condemnation of dowry
A wife should never be purchased. Nor should a father sell his
daughter. Only those persons of sinful soul who are possessed,
besides, by cupidity, and who sell and purchase female slaves for
making serving women, regard the status of wife as capable of arising
from the gift and acceptance of a dowry.
Mahabharata AnusasanaParva Section XLIV
Condemnation of Usury
Bhishma said, ‘They who betake themselves to improper conduct, they
who take exorbitant rates of interest, and they who make unduly large
profits on sales, have to sink in hell.
Mahabharata, AnusasanaParva, Section XXIII
Highest Morality
Tuladhara said, ‘O Jajali, I know morality, which is eternal, with all
its mysteries. It is nothing else than that ancient morality which is
known to all, and which consists of universal friendliness, and is
fraught with beneficence to all creatures. That mode of living which
is founded upon a total harmlessness towards all creatures or (in case
of actual necessity) upon a minimum of such harm, is the highest
morality.
(Mahabharata Santi Parva Section CCLXII
Need to feel for the afflicted
I abide in all beings as their inner-most soul. Disregarding My
presence within them, men make a show of worshiping Me through images.
If one disregards Me present in all as their soul and Lord but
ignorantly offers worship only to images, such worship is as
ineffective as a sacrificial offering made in ashes. A man who
persecutes Me residing in others, who is proud and haughty, who looks
upon God as the other – such a person will never attain to peace of
mind. If a man disregards and persecutes fellow beings, but worships
Me in images with numerous rituals and rich offerings, I am not at all
pleased with him for proffering such worship. A man should, however,
worship Me in images, side by side with discharging his duties, which
include the love of all beings, until he actually realises My presence
in himself and in all beings. As long as man is self-centred and makes
an absolute distinction between himself and others (without
recognizing the unity of all in Me, the Inner Pervader), he will be
subject to the great fear of Death (including every form of
deprivation of self-interest). So overcoming the separateness of a
self-centred life, one should serve all beings with gifts, honour and
love, recognising that such service is really being rendered to Me who
reside in all beings as their innermost soul.
Srimad Bhagavata Purana III.29.21-27
Moral guidelines for the Righteous
Yudhishthira said, ‘Abstentions from injury, the observances of the
Vedic ritual, meditation, subjugation of the senses, penances, and
obedient services rendered to the preceptors - which amongst these is
fraught with the greatest merit with respect to a person?’
Vrihaspati said, ‘All these six are fraught with merit. They are
different doors of piety. I shall discourse upon them presently. Do
thou listen to them, O chief of the Bharatas! I shall tell thee what
constitutes the highest good of a human being. That man who practices
the religion of universal compassion achieves his highest good. That
man who keeps under control the three faults, viz., lust, wrath, and
cupidity, ,,, (and practises the virtue of compassion), attains to
success. ……. That man who regards all creatures as his own self, and
behaves towards them as towards his own self, laying aside the rod of
chastisement and completely subjugating his wrath, succeeds in
attaining to happiness. ….One should never do that to another, which
one regards as injurious to one’s own self. This, in brief, is the
rule of righteousness.
Mahabharata Anusasana Parva Section CXIII