Allah forgave Adam in the day of Ashura. Ibn Rajab said in Late'f al Marif: 

When Adam descended from paradise, he cried for all the things he lost there. It was said that he cried for three hundred years and of course he had the right to do so. He had been in a place where he would never feel hungry, thirsty or naked.  When he descended to earth, he felt the hunger, thirst and nakedness and when he saw Gabriel, he remembered what he used to get from his Lord and cried more until Gabriel cried for Adam's crying and said, "O Adam! Why are you crying?"  Adam said, "How could I not cry when I was removed from the blessed home to a home of misery?"  Some of his children told him, "You are hurting the people with your crying." Adam said, "I cry for the voices of the angels around the Throne." 

In a different narration he said, "I cry to be close to Allah."

Adam knew the happiness of being close to Allah and then suffered the misery of being away from Him. 

If you have a very closed dear friend and you were separated for any reason, you will feel the pain of separation.

The worst separation is the separation from your Lord. 

The prophet (may peace and blessings be upon him) said: "If the slave declared Islam in a good manner (a truthful repentance), Allah will remit every sin he made" (Bukhari). The sins will also be replaced with good deeds. 

The fifth assignment: Protect your sight and hearing with piety.

Allah the all mighty said: {Oh you who believed! If you obey and fear Allah, he will grant you Furqan a criteria [to judge between right and wrong], or makhraj i.e. making away for you to get out from every difficulty], and will expiate for you your sins and forgive you and Allah is the Owner of the great Bounty}.  _{(Al-Anfal:29).} 

Allah the all mighty also said: "And whoever fears Allah and keeps his duty to Him, He will remit his sins from him, and will enlarge his reward". _{(Al Talaq:5).}

In the day of Ashura, make sure you watch what your eyes are looking at, what your ears are listening to and where your heart is going.

Create a plan for yourself to engage you in worshipping and in obeying Allah.  Go early to the prayers and try to stay in the Masjid between Asr and Maghrib.  It is a great day especially as you will be fasting and your supplications will be answered if Allah wills and hopefully when you break your fast, your prayers will be accepted.   

The sixth assignment: Repair the obligatory duties.

Repair or reform your obligatory rituals and Nawafel (extra deeds).  The prophet (may peace and blessings be upon him) said: "The five prayers, Friday to Friday and Ramadan to Ramadan are remittances" _{(Sahih Muslim)}.

If you repair your obligatory rituals, your sins will be expiated.

And it is not only a question of praying on time or going earlier to the prayer. It starts from the beginning, from submitting while performing ablution and praying to Allah as He is purifying your body with water to purify your heart with repentance.

It is anticipation in every step you take to the Masjid, lining up in the first line and supplication to Allah. Get into these habits; decide that you will focus in your prayers and get closer to Allah. 

Repair your Nawafel too. Praying in the middle of night is very important, especially the ninth and tenth night.

If a person repairs their nights, Allah will repair their days. The prophet (may peace and blessings be upon him) said: "Pray in the middle of the night. It is your ancestors' deed and it is a closeness to your Lord, it is an expiation to the sins and a preventive to fault" _{(Sunan At-Termedhei).} 

Source: The Day of Ashoura: A Second Chance? .. written by http://www.manhag.net/trjmh-alshykh-hany-hlmy.html - Sheikh  Hany Helmy .