The key to distinguish between up and down is the last word. According to the rules, the last word in the upper part must end in a light tone (three or four tones in Mandarin) and the lower part in a flat tone (one or two tones in Mandarin).
In this pair of couplets, the word "Gui" is "Cuo" and the word "Xiang" is "Ping".
When pasting couplets, the upper couplet is pasted on the right, the lower couplet is pasted on the left, and the left and right are bounded by the gate or pilaster. This post is because straight books go from right to left, so reading couplets also goes from right to left.