How to paste couplets?

The steps of pasting couplets are as follows:

1. Distinguish the upper and lower heads of the door: when facing the door, the right hand direction is the upper head and the left hand direction is the lower head. When pasting couplets, paste the first couplet and the second couplet.

2. Distinguish between the upper couplet and the lower couplet: according to the tone of the couplet, which one is flat (the last word of the upper couplet is faint, and the last word of the lower couplet should be flat), the causal relationship ("cause" is the upper couplet, and "effect" is the lower couplet), the time sequence (time is the upper couplet, time is the lower couplet), and the spatial scope (the smaller one is the former and the larger one is the latter)