How does Shelley follow traditional practices in "To a Skylark," and where does he deviate from them?

Shelley largely follows traditional practices in this poem. An ode appreciates or commends something or someone. This poem is an ode because it celebrates the skylark, and it uses apostrophe, which means it addresses the skylark directly. These are traditional poetic forms and devices. It is also lyrical in that expresses the speaker's deep emotions about the skylark. It also uses a regular rhyme scheme: ABABB.
What is unusual is to have five-line stanzas, and adding to the unconventionality is the fact that the fifth line in each stanza has a different meter from the first four. The first four lines are in trochaic trimeter. Trochaic means the emphasis or stress falls on the first syllable in the beat: for example, in the line—

Hail to thee, blithe Spirit

—the beat falls on "Hail," "thee," and "Spir." The line is a trimeter because it has three two-syllable beats.
However, the final line in each stanza reverses the stresses. These lines are iambic, meaning the stress falls on the second syllable. Also, they are longer lines in that they have six beats instead of three. They are in iambic hexameter.
But despite these oddities, the poem is largely traditional in form and rhyme scheme, as well as in subject matter.