Birshut HaRav: We are still in Simon 403, the Rama there talking about the Ten Days of Teshuva in terms of their main purpose: that every person should carefully inspect all of his deeds and turn from them or to return from them during the Ten Days of Teshuva. "Return" here means "to return to Hashem; to return to the right path;" "turn from them" meaning "turn away from the misdeeds that we do." The Mishna Brurah brings in a wonderful reference from the Chayei Adam [Listen to Audio for this an all Hebrew Quotations] and explains that the Chayei Adam expounds on the idea of Teshuva. The Mishna Brurah describes his exposition there as being "a salve to the eyes" in that the Chayei Adam describes Teshuva in such a clear way.
What the Chayei Adam does there is he goes through the vidui that we say both in selichot and on Yom Kippur and expounds on each of the 24 words of the vidui. He takes each word and essentially asks, "What's the idea of Teshuva? Yes, we are guilty — but he makes that idea personal and practical and gives us things to think about in terms of our Teshuva.
On a similar note if you look in the back of the ArtScroll Yom Kippur Machzor, there is a similar exposition. ArtScroll takes the vidui — not just the "Ashamnu Bagadnu" but also the longer vidui the al chet — and they go through each line and they make it real and personal. For example, instead of reciting a vidui for killing, ArtScroll takes the idea of killing and makes it personal in a way that we have all participated in and can relate to. Consider a little recommended reading, not only in terms of preparation for Yom Kippur but recommended reading for the Ten Days as part of the vidui we recite during the selichot.
Finally, paragraph 24 in the Mishna Brura. The Mishna Brura writes [Hebrew]. Someone who hired his friend to go travel somewhere, presumably to go do business on his behalf and the hired friend gets killed while he is out conducting the business, says the Mishna Brura, "It is proper for me to do Teshuva for this."
At first glance we no doubt all agree that such a person did nothing wrong, but Chazal have a much more expansive idea of responsibility than we do. We are responsible not only for ourselves but for others as well, certainly for all Jews and even for the entire world. Every small action can have tremendous implications. We should in this particular case be spending time thinking about why it was that this person was killed while traveling on my business? What did I have to do with it? In fact, this is a Torah approach to all puraniut in this world — the Torah way is to look inward at ourselves and ask, "What did we do that caused that?"
The Mishna Brura then goes through aveira after aveira, some of which we would recognize as aveirot and others that we would not, and gives sources of where to look to learn how to do Teshuva for each. These are not sources of the Mussar books of the Middle Ages that advocate things like lying on top of anthills and rolling in the snow. The sources here are sources like the Chatam Sofer, very modern sources that are highly relevant to us in so many areas of halacha. There are many, many such sources to look at either for particular deeds for which we may want to do Teshuva or for general ideas of Teshuva. If you want some more recommended reading you can speak with me privately.
Finally, the Rama brings words that are simply terrifying. [Hebrew] A doubtful aveira, an aveira that I may have committed or may not have committed, or an action that may or may not have been an aveira — such an action requires even more Teshuva than an aveira that I clearly committed that is clearly an aveira. Why? Says the Rama, because one has greater regret when he knows he did something and he knows it was rong than he has when he doesn't know or when he isn't sure. The Rama brings as proof that the Korban Asham and Asham Talui was brought when it wasn't clear whether a person did an aveira or not. If it later became clear that the person did an aveira, he would then bring a chatat. If it became clear that he didn't do an aveira, he was then clear; and if it remains a sofek, he was clear by the Asham Talui. An Asham Tolui was much more expensive than a chatat offering. The Rama brings this down as proof that that which is a sofek requires more intense Teshuva than that which is vodai. According to the note iin the text, this is the Rama's own idea, though there is a reference that refers us to Rabbeinu Yonah in the beginning of Masechet Brachot.
I will also refer us to a pasuk from last week's parsha. [Hebrew] "Those aveirot that are hidden from us are the ones that Hashem takes accounting of; those aveirot that are revealed to us, those are the ones that we have the responsibility for owning and doing Teshuva for. If you want to keep your aveirot from causing judgment against you at the hands of the Heavenly Court, the simple solution is to remain conscious of your aveirot and do Teshuva for them yourself — a very difficult task, but nonetheless one to which we should aspire.