Immersion
Every Jew is required to immerse in a mikvah on the day before Yom Kippur in respect for the sanctity of the day and so as to repent and be purified of sin. This practice dates back to the time of the Prophets. According to the Geonim, the immersion should be preceded by a blessing, but it is not our custom to do so.
Candles
It is customary to light a 25-hour memorial candle in the synagogue. This candle is called "The Candle of Life". If one's parents are not living one lights an additional 25-hour memorial candle in one's home. This candle is called "The Candle of the Soul".
When the Festival candles are lit, two blessings are recited: L'Hadlik Ner Shel Yom ha-Kippurim, and She-hechiyanu.
Blessing Children
Before entering the synagogue, it is customary for fathers to bless their children. Although there is no required formula for this blessing, it is customary for fathers to say:
May G‑d make you like Efrayim and Menashe [for a son]; or, May G‑d make you like Sarah, Rivkah, Rachel, and Leah [for a daughter].
The Lord spoke to Moses, saying: Speak to Aaron and to his sons, saying: This is how you shall bless the children of Israel. Say to them: "May the Lord bless you and guard you. The Lord make His countenance shine upon you and be gracious to you. The Lord turn His countenance toward you and grant you peace." They shall bestow My Name upon the children of Israel, so that I will bless them.
Some also add the following text:
May it be the will of our Father in Heaven to place into your heart love and fear of Him. May the fear of G‑d be upon you always so that you never sin. May your yearnings be for Torah and mitzvot. May your eyes see straight ahead, may your mouth speak wisdom, and may your heart feel awe.
May your hands engage in mitzvot, your feet run to fulfill the will of your Father in Heaven. May He grant you sons and daughters who are righteous, who will be engaged in Torah and mitzvot throughout their lives.
May your livelihood be blessed and may your sustenance be earned in a permitted manner, with ease and bounty from His generous hand, rather than from the gifts of flesh and blood; sustenance that will leave you free for the service of G‑d. May you be inscribed and sealed for a good and long life among all the righteous of Israel, Amen!
Please be aware that some of these practices differ, depending on one's Jewish Heritage...only men go to the mikvah on Erev Yom Kippur. In my husband's family every woman lights a yarzheit candle when she lights for yom Kippur, regardless of whether or not parents are living, and both fathers, mothers and if possible, grandparents bless the children.
Women and Mikveh, Erev Yom Kippur and After To Anonymous in Passaic and London:
Some women in our Lubavitch kehilla go to the mikveh erev Yom Kippur. What a privilege and purifying experience! We are dipping into the "womb" of G-d and emerge pure as a newborn baby. This is before Yom Kippur. After Yom Kippur, after we have fasted and afflicted ourselves and Hashem has forgiven us for our aveiras, the challenge is to keep that exalted level we achieved on Yom Kippur. One way is to eat for the energy to serve Hashem instead of eating for physical pleasure, right from the start, right from the break fast, and on.... That way we strengthen our G-dly soul instead of strengthening our animal soul.