On the writing of sonnets

In an article on the Athenaeum Hectoris blog, Master Hector of the Black Height, of the Kingdom of Ealdormere, discusses the basics of sonnets and sonnet writing, including rhythm, phrasing and form, in the article Missive to a Young Poet: Sonnets.

From the article:

Form fits function and ultimately the sonnet is a dialectic structure. It is designed to shape logical analysis of a problem, to provide a venue for dynamic argument and resolution and then to guide the writer through to a conclusion, and if you do it right it’ll make some art in the process. As a form the sonnet consists of two main blocks of text, the octet (first eight lines) and the sestet (last six lines). As a general rule, the octet splits into two four-line quatrains, defined by the rhyme scheme. The sestet splits into a third quatrain and a final couplet. Thus the fabulous sonnet rhyme scheme,

ABAB CDCD EFEF GG

that probably was beaten into you at some stage of your high school education.
If you want to look at the sonnet as a poetic syllogism, the octet sets forth the thesis. The third quatrain that opens the sestet sets for the antithesis and then you sum up in the last couplet, the synthesis.