How to Confirm the ‘Dālah of an Imam
It is enough to confirm the ‘dālah (justice) of the imam of the congregational prayer through any possible way, even through seeing some insightful and righteous people praying behind him. Rather, the apparent goodness is also enough to consider him as ‘ādil. However, when his being ‘ādil is verified, a later doubt about it does not prevent from praying behind him.

To Lead Prayer While Not Considering Himself as ‘Ādil
There is no problem in leading congregational prayer by a person who does not consider himself as ‘ādil and congregational prayer is valid provided that those who follow consider him as ‘ādil. He may intend not to lead the prayer. In this case, his prayer as well as those of who follow him are valid. 

To Lead Prayer with Tayammum
A person, who is exempted from ghusl, may make tayammum instead of ghusl and lead congregational prayer. It is permissible for others to say their prayer behind him.

Leading Prayer While One's Hand Is Amputated
In case a person's a hand or foot is completely amputated or paralyzed, his leading the congregational prayer is problematic. However, amputation of some fingers/toes — even the big ones — does not harm his leading the congregational prayer.

A Woman's Leading Prayer
In congregational prayer, a woman may only lead a congregation of women.

To Prayer behind a Layman
Whenever a Muslim clergyman is available, one should not pray behind a layman. However, if there is no clergyman, praying behind a non-cleric who meets the conditions of leading a congregational prayer is no problem.

To Pray behind a Person with Doubted Recitation
Observing the rules which provide betterment of pronunciation is not necessary. If Arabic speakers consider the recitation of the imam of congregational prayer as correct, it is permissible to follow him. In case of doubt, following him is valid as well.

To Pray behind a Sunnī Imam
It is permissible to perform one’s prayer in congregation behind a Sunnī imam for the sake of maintaining Muslim’s unity and the prayer is valid. 

During Recitation of the Imam
In the first and second rak'ah of 'noon' and 'asr prayers, the follower should not recite the two chapters. It is mustaḥabb for him to say dhikr. In morning/maghrib and ‘ishā’ prayers, the follower should listen to imam's recitation if they can hear his voice even as humming; otherwise, it is mustaḥabb that they themselves recite the two chapters.

Imam's Omitting a Verse
 If the imam in congregational prayer does not recite a verse of the surah, the follower informs him – like through saying a dhikr or a verse; otherwise he changes his prayer into individual prayer and recites the chapter.

Prayer around Ka'bah
Around ka'bah, prayer of those standing behind the imam or at his left/right side is valid but that of followers standing in front of the imam is invalid.