Generally speaking, traditional brush calligraphy is written vertically from right to left, and does not need to be arranged according to lines of poetry. If it is a banner, four lines of poetry can be written in two rows and so on.
If written with a hard pen, it can be written in the traditional vertical banner form or in the horizontal form. In the horizontal form, for the sake of neatness, it is generally written in lines of poetry.
However, there is no absolute rule, as long as the layout is beautiful and beautiful.