Preparation. Take some time to look over the Yom Kippur prayer book. Read the translation. Get to know the atmosphere of the prayers, and when you encounter them in synagogue they will be more meaningful.
Define what you need to correct. Sins are one thing. They are an obvious target for repentance. What is more important are character traits. Things often come as a result of character traits. I remember learning that all sin in the trace to one of three character challenges: jealousy, lust, and pride. Working on one's character is the most important work of Yom Kippur. Being aware of where we get into trouble and why is the first step. Deciding on concrete steps to grow and improve is the next step.
Apologize to God. This refers to all of the sins that relate between man and God. If someone wasn't careful about keeping kosher, they should admit their shortcoming in prayer and decide to improve in the coming year. If someone didn't pray as well as they could have, they should mention this and determined to improve their prayer in the future.
Apologize to one's fellow. Yom Kippur atones for those sins that are directly between man and God. For sins that one has committed to another, one must first obtained the other's forgiveness. Jewish law states that a person should ask forgiveness a maximum of three times. If the other refuses to forgive, one need not ask a fourth time. Nonetheless, if someone asked for forgiveness, we should be forthcoming with it. Nobody should want someone else to be punished on their account. Only after properly asking forgiveness from the other can we then ask God for forgiveness.
An interesting problem is when one has spoken slanderously of another. If the other does not know about it, to tell them in order to apologize might cause more harm than good. In that case, it is best to give a general apology, and not hurt the other person's feelings by sharing what was said. One should, however, seek to undo whatever damage was done by ill considered speech.
Dress appropriately. Create the atmosphere for spirituality. On Yom Kippur, we refrain from wearing leather shoes. It is also appropriate to wear white clothing, if possible. White is the color of purity, and creates an atmosphere of great spirituality.
Eat a proper meal before the fast. Drink adequately, but do not overeat. I have had a Kol Nidre night challenged by a stomach that was unhappy with the way I ate before the fast.
Prepare to be in a good mood. The Divine Presence comes where there is joy. For that reason, Yom Kippur, with all of its solemnity, carries inside a deep joy. Sing along with the Cantor, and let the beauty of the prayers fill your soul. I remember seeing someone so uncomfortable in synagogue that they laughed at every ritual. This is very sad. It may be an effort, but it is so important to open oneself to what is happening in synagogue. Even if you don't attend during the entire year, and don't really know what is going on, make a mental decision to be open to try to sing along, to reading the prayers in English, to saying them with as much sincerity as you can muster.
Maintain the dignity of the day. What you do when you leave the synagogue? How about keeping the television off? Try creating an atmosphere of sanctity and quiet in your home throughout the day. Don't plan to travel or distract yourself with novels or music or anything else. Consider taking a quiet walk, meditating, or reading about self-improvement or the meaning of the day.
Be in synagogue as much as possible. You will be surrounded by people deeply connecting to Yom Kippur. You'll be surrounded by strong Jewish feeling, melody, prayer, and inspiration. Stay after the memorial service for a little bit, if you can. Avoid meaningless conversation. Be present to Yom Kippur for as much of the day as you can, and Yom Kippur will be present in your life for a whole year!
I wish you all and easy fast and a healthy, happy, and successful year. May you be properly sealed in the Book of Life!