Capitalization and punctuation are often tricky things in poetry, as there is no definitive right and wrong way to incorporate them into a poem. A prose (non-poetry) selection which does not adhere to the conventions of capitalization and punctuation would be seen as non-sensical and virtually impossible to read. A poem is much different in that it is already written in a kind of condensed format and thus our expectations for those conventions are quite different.
The one fairly consistent rule for all poetry is that the first word in any line of poetry is capitalized, though of course not every poet adheres to that rule. Aside from that, the capitalization rules are generally consistent with prose writing. Commas, periods, semi-colons, dashes and quotation marks serve roughly the same functions in a poem as they do in prose.
The poem I chose for you is a sonnet titled "Ozymandias" by Percy Bysshe Shelley. (Note that poem titles are in quotation marks.) It contains many examples of both correct punctuation and capitalization and provides some excellent examples of literary devices.
I met a traveller from an antique land
Who said: "Two vast and trunkless legs of stone
Stand in the desert. Near them, on the sand,
Half sunk, a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things,
The hand that mocked them and the heart that fed.
And on the pedestal these words appear --
'My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!'
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare
The lone and level sands stretch far away.
Analysis: The once-mighty Ozymandias created a "colossal" monument as a testimony to his greatness and vast empire; now, centuries later, all that is left is the "colossal" wreckage. The point, of course, is that even great things made by great men do not, cannot last, so boasting of them as if they could is foolishness.
Capitalization: Consistent both with writing and poetry rules. The first word of each line is capitalized, as is the proper noun, Ozymandias. The one anomaly is the word "Mighty," which is a kind of proper noun, referring to all the other leaders of the day who he hopes to intimidate with this statue.
Punctuation: Also generally consistent with prose. When a thought ends, he uses a period; otherwise, he uses whatever most suits his message. Notice that a colon introduces a long direct quote and a dash is used for effect. Both double and single quotations marks are correctly used. For American English, double quotes are used first; if the quote contains a quote (as this one does), use single quotes. Also note that the exclamation point is inside the single quote because it is part of that quote.
This poem is am Italian sonnet and adheres to the sonnet form. It is also full of imagery (appeals to the senses). Those are easily observed.
The poem utilizes dramatic irony. Ozymandias obviously intended for this grand work of art to serve as a testament to his great achievements as well as a warning to potential invaders; now it is both a testament and a warning that great things (even works of art) eventually fall and crumble.
Also note the use of synecdoche (using a part to represent the whole). "Visage" (meaning face) is used to represent the entire head of the crumbling statue. "Hand" is also representative of the one who created it, the sculptor.
While very long, The Waste Land by T.S. Elliot is a very good example. Eliot uses months and flowers to symbolize the aftermath of the war. He created a very eloquent picture for his readers. He uses different languages to give the poem depth and alternate meanings, while keeping it fairly easy to understand. He uses many commas and capital letters in places that aren't entirely necessary.
Acquainted with the Night by Robert Frost
I have been one acquainted with the night.
I have walked out in rain—and back in rain.
I have outwalked the furthest city light.
I have looked down the saddest city lane.
I have passed by the watchman on his beat
And dropped my eyes, unwilling to explain.
I have stood still and stopped the sound of feet
When far away an interrupted cry
Came over houses from another street,
But not to call me back or say good-by;
And further still at an unearthly height
One luminary clock against the sky
Proclaimed the time was neither wrong nor right.
I have been one acquainted with the night.
This poem makes use of capital letters to start off each line. That's one way to make use of capitalization. It has a steady A,B,A,B rhyme pattern. His use of commas, periods, and semi-colons is similar to the way one would use them in prose.