What did Imam used to advise believers to observe during Ramadan?

Pay attention to our own flaws.

Imam's books and works contain treasure of divine-oriented wisdom

Islamic scholars, motivated by a tradition from the Prophet Muhammad, which promises Divine Rewards for scholars who collect forty traditions, compile hadith narrations in groups of forty.

Imam Khomeini: You have been invited to the God feast; you are His guest in the month of Ramadān.

Sahifeh-ye-Imam. V 13. P 27-28

The blessed month of Ramadān and the invitation to the Almighty God’s feast.

The blessed month of Ramadān and the invitation to the Almighty God’s feast.

The invitation of the blessed Ramadān

The sacred month of Ramadān is ahead; a month in which you should strengthen yourself morally.

Imam Khomeini showed great devotion towards Quran during Ramadan

Imam Khomeini, the late founder of Islam Rebublic, attached great significance to reciting the holy scripture of the sacred divine scripture of Quran during the blessed month of Ramadan