Shelley gives his poem "Cloud" a lyrical quality mainly through the use of rhyming patterns that make it read like a ballad, or a song that is told almost as a story. Throughout most of his poem, he uses the rhyming scheme, abcb, which means that the lines ending in b rhyme. For example, look at the following four lines, and how they rhyme:
"I bring fresh showers for the thirsting flowers,/From the seas and the streams;/I bear light shade for the leaves when laid/In their noonday dreams."
In this stanza, the 2nd and 4th lines rhyme-"streams" and "dreams". There is also rhyming within each off-line (so, lines 1, 3, and 5, etc.). Note the internal rhymes within line 1: "I bring fresh showers for the thirsting flowers." So, showers rhymes with flowers. Then, in line 3, "shade" and "laid" rhyme. That makes it so that almost every single line of his poetry has a rhyme in it-either internally, or in the end words that match up with every other line.
If you listen to any song lyrics, rhyming is a main feature that gives them their song-like quality. So, through the use of rhyming, Shelley creates a song-like feeling to his poem. As you read through it, the rhyming gives is a rhythm and sound that is very lyrical. His rhythmic beat is varied throughout the poem, so that doesn't make it as lyrical as the rhyming does. As a person reads a poem with rhyming in it, they naturally add pauses, rhythm and a beat, which gives it its meter and lilt. So, the rhyming makes it lyrical, and also aids in it being read with a rhythm, all which make the poem very song-like and lyrical. I hope that those thoughts helped!