Poetry (communicate) in words. To do that (successful), it must have something important to say, expressing it in a unique way. Whether you are writing poetry yourself or analysing (分析) poems (write) by someone else, you should be thinking about these two broad categories: what is being said, and how it is being expressed.
What is being said may be something unforgettable or something funny, something deeply emotional or something that has just made the writer stop and think. Whatever it is, the theme of the poem will be something worth (say). If you are writing a poem yourself and are not very (experience), it's best to choose a topic you feel deeply about. Writing a poem begins with ‘I remember' is a good way to focus your attention something really memorable.
However, two poems could easily have same theme and yet be completely different. What makes (they) different? How they are expressed is the key. It is the way the poet writes that you need to analyse if you are writing about a poem, and if you are writing one yourself, you must choose the form and the words which suit what you want (express).