(I will change the title and some words to Chinese when I get home)
I can think of two fundamental rules:
1. One must acquire the voice of the poet. That is, to speak like the poet being translated. I saw a number of English translations of Li Bai's works, but none sounded like Li Bai. The translators seemed more interested in demonstrating their skills with the English language and showing how "cultured" they were.
2. One must acquire the "mechanism" of the imagery in the poem. Some poems have flying imageries (such as those of Li Bai), some flowing (such as Bai Ju Yi), some rushing, some hesitating, some leaping (such as Li He4) , some stationary (such Du4 Fu3) , and so on. One is not supposed to turn a flying poem into a leaping one, a flowing one into a stationary one, for instances.
In my reading experiences, most translations fail these two basics. Therefore the basic may well be the most challenging.
The rest such as rhyme, meter ... are all much less important or sometimes even superfluous in my observation. Often they do not translate from language to language, from culture to culture. If one draggs them through, during the struggle, one likely loses the voice and the mechanism of the imagery altogether. So, no need to labor it.