When we talk about a poem's translation one might say that it is impossible to be 100% faithful to the original piece of work. What do I have to take into account when I'm translating a poem? What makes a good translation of a poem?
Part of what makes a translation "good" has to do with its purpose. In general, translations fall along a spectrum of purposes, from those attempting to convey the most literal possible sense of the original to those which take the original as a starting point for what is often almost writing an original poem in the target language. Which you choose to do depends on your audience. If you are publishing a translation in a textbook, or doing a translation for a language class, you might want to focus on literal meaning, while if you are publishing in a literary magazine or writing for a poetry workshop class, creating a good poem in the target language is a more important goal.
Next, you need to deal with the concept of cultural equivalency. For example, when translating Greek and Latin epic into English, you have the dilemma that dactylic hexameter is the standard meter for Latin and Greek epic, and in those languages sounds "natural". The problem is that the most common meter for long poems in English is iambic pentameter. Thus you have the choice of whether to stick with dactylic hexameter as the "original" meter (something really hard to do as it is an awkward meter in which to write in English), or whether you might consider iambic pentameter as culturally more analogous.
Another issue you will need to address is specificity of references. For example, much of the humor in Latin satire has to do with references to figures completely unknown now. Do you want to add footnotes or somehow change the names to be more generic or substitute modern references? Idioms are similarly problematic, with literal translations often being confusing to readers.
Basically, as a translator, you are always making difficult choices -- that is what makes literary translation so challenging. You have the duty to remain as faithful as you can to the voice of the original, but you also want to create a good poem for your readers. A good way to think this through is to look at several different translations of the same poem (Homer is ideal, because they are so many) and compare them to start seeing how translators make choices and how they affect your reading experience.