1. The Gemara discusses stringencies that righteous people took upon themselves which caused them to live a long life.
2. One of these stringencies was not attaining honor through someone else's degradation.
3. Another meritorious stringency was making sure that one did not underpay.
4. One who forgives others is forgiven by Hashem for all of his sins.
5. One is forbidden to look at the image of an evil person.
A BIT MORE
1. The students of these righteous people asked them, towards the end of their lives, how they merited to achieve such a long life. The elders all answered that they believed it was due to various stringencies they had accepted upon themselves.
2. For example, a person should not allow an important person to publicly serve him if this person does not usually serve people in public.
3. If there was any question about whether a storeowner's weights were accurate or whether he owed a little more money, he would immediately pay that extra money.
4. The verse states, "He carries sin, and passes over sin." The Gemara derives, "Whose sins does Hashem carry? The sins of someone who passes over (i.e. forgives) others who sin against him."
5. The Gemara says that this contributed to Yitzchak Avinu becoming blind, since he constantly looked at Esav.