Some relevant laws related to this High Holy Day season taken from the Rambam's Hilchos Teshuvah (Laws of Repentance).
There are twenty-four things that impede teshuvah (repentance) that we would do well to consider and take to heart. Four of them are such great sins, that the one committing them is in danger of not being afforded the opportunity to repent:
(i) Causing the public to sin or preventing the public from performing a mitzvah.
(ii) Influencing another person to turn away from the good way to the bad.
(iii) Seeing one's own son going out to evil ways and failing to admonish him.
(iv) Saying, "I shall sin and I shall repent," or "I shall sin and Yom Kippur shall atone."
Five other sins hinder the path of teshuvah from those who commit them:
(v) Separating oneself from the congregation for [by doing so] . . . he will not benefit as they will benefit.
(vi) Disputing the words of the Sages, for his dispute will cause him to separate himself from them, and he will remain ignorant of the ways of teshuvah.
(vii) Mocking the mitzvot.
(viii) Insulting one's own Torah teachers, for . . . one who does so will not find anyone to teach him and to show him the true road.
(ix) Abhorrence of admonition and correction, for it is admonition that brings about teshuvah.
Five other sins make it impossible to do complete teshuvah, for they are sins against another person, but the person does not know against whom he has sinned, to whom he must make restitution, and from whom he must ask forgiveness:
(x) Cursing the public.
(xi) Sharing stolen property with a thief, thus not knowing to whom to make restitution.
(xii) Finding an identifiable object and not advertising it so that it may be returned to its owner; if he seeks to repent after a period of time, he will not know to whom to return it.
(xiii) Unlawfully taking and eating that which belongs to paupers, orphans, or widows, or other such unfortunates who are not well known and often are homeless, having to wander from city to city, so that the thief will never know to whom he must make restitution.
(xiv) Accepting a bribe to bend the law, for one can never appraise the ramifications and loss caused by bribery, and will therefore not be able to rectify the matter completely.
Another five are sins for which the one who commits them will most likely not repent, for most people do not consider them wrong; thus one sins, but does not become aware of his guilt:
(xv) Eating from a meal that is insufficient for it's owner, for the perpetrator thinks, "I have not eaten anything without permission."
(xvi) Using a poor man's tools, such as an ax or a plow, that one holds as a pledge, for one will say, "They are missing nothing; I have not stolen from them."
(xvii) Gazing lustfully at women, for one thinks he has done nothing wrong, and says to himself, "I have not had relations with her or even touched her," unaware of the great sin he has committed with his eyes.
(xviii) Glorying or rejoicing in another person's degradation, for one thinks that he has not sinned so long as the other is not standing before him and therefore is not embarrassed.
(xix) Suspecting innocent people, thinking that such suspicion is not sinful, and saying, "What have I done wrong? Have I done anything more than raise a possibility - maybe he did it, maybe he didn't?" But he does not realize that this is a sin, for it takes an innocent person and turns him, albeit only in the other's mind, into a sinner.
And the final five are sins that become habitual and it is thus difficult to separate oneself from them; so a person must be especially careful and scrupulous to avoid them lest he become attached to them, for they are all extremely bad traits:
(xxiii) Thinking evil.
(xxiv) Friendship with the wicked, with whose deeds he will become familiar and they will become impressed in his heart.
All these twenty-four things and their like, despite the fact that they hinder and impede teshuvah, do not prevent teshuvah. Rather, if one does succeed in repenting from them, he is a penitent and he has a share in the World to Come.
Let him who is convinced that his views are true and right express them . . . at every opportunity . . . without considering how much support or how much opposition he will encounter. Only falsehood is in need of many supporters in order to win the day; falsehood must have the authority of numbers to make up for what it lacks in justification. Truth, by contrast, will always prevail, even if it takes time. Noble, courageous and pure, expressed with all the fiery zeal and conviction and with all clarity of sure awareness, stated again and again at every opportunity, truth will ultimately gain respect and admiration even of those who do not accept it. The only truth that can be lost beyond recall is that truth whose adherents no longer have the courage to speak up candidly on its behalf. Truth has never gone down in defeat as the result of opposition, it has done so only when its friends are too weak to defend it. - R' S.R. Hirsch