My close friend (may Allah's peace and blessings be upon him) advised me with three: fasting three days of every month, the two Rak‘ahs of Duha, and performing Witr before I sleep

The Prophet (may Allah's peace and blessings be upon him) gave his Companions different pieces of advice based on his knowledge of their conditions and what suits each of them, as Jihad is suitable for the strong one, worship is suitable for the devoted worshipper, knowledge is suitable for the knowledgeable, and so on.
Ibn Hajar al-‘Asqalāni said about his statement: (fasting three days of every month); this apparently refers to the White Days, namely the 13th, 14th, and 15th of the Hijri month.
Ibn Hajar al-‘Asqalāni said: It signifies that it is recommended to pray Witr before sleep for the one who is not confident about waking up.
The importance of these three deeds, given the fact that the Prophet (may Allah's peace and blessings be upon him), advised a number of his Companions to observe them.
Ibn Daqīq al-‘Eid said about his statement: (the two Rak‘ahs of Duha): Perhaps he mentioned the minimum with which the deed is confirmed, and this indicates that the Duha prayer is recommended and that its minimum number of Rak‘ahs is two.
Time of the Duha prayer: It starts almost 15 minutes after sunrise, and its time extends to almost 10 minutes before noon. Its number: Its minimum number of Rak‘ahs is two; however, there is a difference in opinion regarding the maximum; it is said: eight Rak‘ahs, and it is said: Its maximum has no limit.
Time of Witr: It starts right after the ‘Ishā’ prayer until the break of dawn. Its minimum number of Rak‘ahs is one, and the maximum is eleven Rak‘ahs.