A great day begins with small details. Make sure you're on top of things:
1. Yom Kippur begins today, Sunday late afternoon, and continues until Monday evening. It's recommended to check the exact start and end times of the fast wherever you are, in Israel and around the world. These are extraordinary hours - no eating or drinking, no leather shoes, no cell phones, no commerce or cars - but with prayer, forgiveness, soul-searching, and renewal. The Torah writes of the day ahead of us: "For on this day He shall atone for you, to purify you; from all your sins before God shall you be purified." This is a day God gave us to atone for and cleanse all our sins, all our failures and mistakes. After it, we begin again, pure.
2. Yom Kippur is the only day of the year with five prayer services: Ma'ariv (evening), Shacharit (morning), Musaf (additional), Mincha (afternoon), and Ne'ilah (closing). The most famous passages are "Kol Nidrei" and "Ne'ilah," and there are many other elevated sections as well. It's worth going over the prayer machzor (prayer book) in advance, asking others for help, or being someone who offers help to those less familiar with it.
3. Today, up until Yom Kippur begins, there are many customs and laws - people traditionally perform Hatarat Nedarim (annulment of vows), Kapparot redemption, ask forgiveness from family and friends, give charity, visit the cemetery to visit the graves of relatives and pray, recite a special early Mincha prayer with Vidui (confession), light candles with a special blessing, and parents give the "Blessing of the Children" - among other customs.
4. Note: before the fast, one eats the Seudah HaMafseket (the final pre-fast meal), but there is also a mitzvah to eat throughout the day until the fast begins. The final meal itself is considered joyous and festive. Our commentators explain that it would have been fitting to hold a festive meal on Yom Kippur itself, since it's such a joyful day of new beginnings - but since it's a fast day, we eat that meal beforehand instead.
5. At the conclusion of Yom Kippur, it's customary to move from one mitzvah straight to the next, so people traditionally begin talking about building the sukkah - and even start building it - as preparation for the upcoming holiday.
Have an easy fast. May we all be sealed for good.