Resist the urge to explain it; let the reader become engaged with the poem in developing an understanding of your experience or message. Avoid the sense that you're stopping there just because you're short of ideas.
This will be a couplet when the final word is penned. Did you catch that meter?! The tercet has three lines. 1 and 2 rhyme, as do 4 and 5, 3 and 6. Show your readers and listeners what you're talking about help them to experience the imagery of the poem. Put in some "sensory" handles. These are words that describe the things that you hear, see, taste, touch, and smell, so that the reader can identify with their own experience. The key, then, is to replace or enhance abstractions with concrete images, things that you can appreciate with your senses: a rose, a shark, or a crackling fire, for example. The concept of the objective correlative may be useful. For example: Hey, I just met you And this is crazy But here's my number So, call me maybe?2 Other poetic devices include meter, metaphor, assonance, alliteration, and repetition. If you don't know what these are, you may want to look in a poetry book or search the Internet.
The last line is to a poem what a punch line is to a joke something that evokes an emotional response. Give the reader something to think about, something to dwell on after reading your poem.