Types of worship and deeds to be performed during the ten days:
One must understand that these days are a great blessing from Allah to His slave, which is appreciated properly by the actively righteous. It is the Muslim's duty to appreciate this blessing and make the most of the opportunity, by devoting these ten days to paying more attention to striving hard in worship.
Among His blessings to His slaves, Allah has given us many ways in which to perform righteous deeds and worship Him, so that the Muslim may be constantly active and consistent in his worship of his Lord.
Among the righteous deeds which the Muslim should strive to perform during the first ten days of Thul-Hijjah are:
1) The performance of Hajj and ‘Umrah, which are the best of deeds that may be done. And what indicates their superiority are a number of narrations, one of which is the saying of the Prophet : "Performance of 'Umrah is an expiation of the sins committed between it and the previous 'Umrah, and the reward of the Hajj which is accepted by Allah, Most-High, is nothing but Paradise." [Al-Bukhari and Muslim]
2) Fasting: It is recommended to fast on the nine days and especially on the ninth day of Thul-Hijjah. There is no doubt that the act of fasting is one of the best deeds, and it is from what Allah, Most-High, has chosen for himself, as in the Sacred Hadeeth: "Fasting is for Me (Allah), and it is I who give reward for it. Verily, someone gives up his sexual passion, his food and his drink for my sake..." [Al-Bukhari, Muslim, At-Tirmithi, An-Nasaa'i and Ibn Maajah]
Also, from Abu Sa'eed Al-Khudri who said that the Messenger of Allah said: "No servant (of Allah, Most-High) fasts one day in the way of Allah, except that Allah, the Most-High, removes his face from the fire because of it (the distance of traveling) seventy years." [Al-Bukhari and Muslim]
The Prophet said: "Fasting the Day of ‘Arafah will be credited with Allah by forgiving one's sins of the previous year and the following year." [Muslim]
3) Uttering the mention of Allah: It is recommended to utter Takbeer ("Allahu Akbar"), Tahmeed ("Al-hamdu Lillaah"), Tahleel ("La ilaaha illallah") and Tasbeeh ("Subhaanallah") during the first ten days of Thul-Hijjah in the Mosque, at home, on the street and every place where it is permitted to mention Allah and mention His name out loud, as an act of worship and as a proclamation of the greatness of Allah, Most-High. He The Most-High, Says (what means): {...And mention the name of Allah on known [i.e., specific] days...} [Quran 22:28]
4) Performing 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, reading Quran, supplicating, 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.
5) Offering 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. It is the Sunnah of our father Ibraaheem - from when Allah The Most-High, redeemed his son by the great sacrifice (of an animal in his place). The Prophet slaughtered (sacrificed) two horned rams, black and white in color, and he slaughtered them with his own hands, mentioned the name of Allah (saying Bismillaah), said Takbeer (Allahu Akbar), and placed his foot on their sides (while slaughtering them). [Al-Bukhari and Muslim]
6) Sincerely repenting: 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.
Repentance means coming back to Allah and foregoing all the deeds, open and secret, that He dislikes, out of regret for what has passed, giving it up immediately and being determined never to return to it, and to adhere firmly to the Truth by doing what Allah loves. The Prophet said: "Verily Allah has a sense of 'Ghayrah' (honor, prestige and anger over violation), and Allah's sense of Ghayrah is provoked when a person does that which Allah has made prohibited." [Al-Bukhari and Muslim]
7) It is incumbent for the Muslim (who is not making Hajj) to make every effort to perform the ‘Eed Prayer wherever it is performed, and to be present for the Khutbah (sermon) and benefit.
He must know the wisdom behind the legislation of this ‘Eed (celebration). It is a day of thankfulness and performing deeds of righteousness. So, he must not make it a day of wildness, pride and vanity. He should not make it a time of disobedience and increase in forbidden things such as music, singing, uncontrolled amusement and the like - those things which could cause the cancellation of the good deeds done in these ten days (of Thul-Hijjah).
There is much to be gained, so make the most of the opportunity afforded by these invaluable and irreplaceable ten days. Hasten to do good deeds, before death strikes, before one regrets his negligence and failure to act, before one is asked to return to life but only when prayers will never be answered, before death intervenes between the hopeful one and the things he hopes for, before one is trapped with his deeds in the grave.