What are the manners of praying behind the Imam and how to align in rows, what is the distance between rows, and does prayer become invalid if it is vast?

The most important things for a congregant (ma'mum) are the intention to follow the imam and to follow him without preceding him or being parallel to him in any pillar. He should also straighten the rows by pressing foot to foot and shoulder to shoulder, and by closing ranks. As for the distance between rows, it is determined by custom, provided there isn't an unusual distance that prevents following the imam. Al-Mardawi mentioned that the estimation of the distance refers to custom, and some interpreted it as three cubits, or such that another row cannot stand in it. As for the Shafi'is, the prayer of anyone in the row is invalidated if the distance between him and the one in front of him exceeds three hundred cubits. Thus, the distance between rows refers to custom, and should be enough for the worshipper to bow and prostrate. If it exceeds three hundred cubits, the prayer is invalidated according to the Shafi'is.