Read the poem. As you read, try to get a general idea of the poem's plot or meaning.
Read the poem again. This time, look for words that indicate contrast, like "however," "but," "still" or "yet." You may want to circle them with your pencil. These words often immediately lead into a shift in which the author shows two sides to an issue. Or, the poet might intend to negate the words he used before the shift.
If you have not found words that indicate contrast, you can find the shift in the poem by looking at the poem's topic. While reading, write down the topic addressed in each stanza of the poem. The point where the poem changes topic is the shift.
You might also search for a shift in tone. A poet might write in a formal tone and shift to slang. Or, the poet could change from a matter-of-fact tone to a sarcastic one. You can find shifts in tone by paying careful attention to the way the language sounds in the poem. In many sonnets, which are always 14 lines long, the first eight lines present a problem or issue, and the last six present a resolution. In a sonnet, then, the shift comes somewhere after the eighth line.