You read a poem for what you will find there, for what it tells you about yourself, your life, your world. The you read it a second time for the pleasure you find in the way the poet uses words. Even if you are not entirely sure that you understand everything in the poem in your first reading, you can be struck by the writer's skill. If we take a very short poem as an example, you can see that it is often the poet's ability to choose one thing out of the mass of small details that brings a poem to life. Other poems can suggest an emotional situation so clearly and with such intensity that you find the words stay in your memory , even if you could not write them down exactly if you were asked.
Longer poems can be more difficult for the reader.
The general rule is to read the poem straight through to the end, even if you are unsure of the meaning of all the words or phrases the first time around. Often the whole poem will clarify the meaning of the early images or lines. Unless you give yourself the opportunity to read the entire poem, you will not have a fair chance to find out what it is saying. It is possible, of course, for you to pay close attention as you follow the words in a poem, read it carefully straight through to the end, reread it a second tie, and still find its meaning elusive. Then you might find writing a paraphrase of the subject of the poem helps you to understand it as you attempt to put the poem into your own words.