The Prophet said, "No good deeds done on other days are superior to those done on these (first ten days of Dhul Hijjah)."
Among the good deeds which the Muslim should strive to do during the first ten days of Dhul-Hijjah are:
- Fasting. It is Sunnah to fast on the ninth day of Dhu’l-Hijjah, because the Prophet (peace and blessings of Allah be upon him) urged us to do good deeds during this time, and fasting is one of the best of deeds.
- Takbeer. It is Sunnah to say Takbeer ("Allahu akbar"), Tahmeed ("Al-hamdu Lillaah"), Tahleel ("La ilaha ill-Allah") and Tasbeeh ("Subhaan Allah") during the first ten days of Dhul-Hijjah.
- Doing more good deeds in general, because good deeds are beloved by Allah and will bring a great reward from Him. Whoever is not able to go to Hajj should occupy himself at this blessed time by worshipping Allah, praying (salaat), reading Qur’an, remembering Allah, making supplication (du’aa’), giving charity, honoring his parents, upholding the ties of kinship, enjoining what is good and forbidding what is evil, and other good deeds and acts of worship.
- Sacrifice. One of the good deeds that will bring a person closer to Allah during these ten days is offering a sacrifice, by choosing a high-quality animal and fattening it, spending money for the sake of Allah.
- Sincere repentance. One of the most important things to do during these ten days is to repent sincerely to Allah and to give up all kinds of disobedience and sin. (islamicity.com)