The Italian poet Petrarch was the pioneer in this direction. The Petrarchan sonnet was a very strict and almost rigid form. Petrarch wrote a series of love poems about an imaginary lady, in a fixed meter and rhyming scheme (abbaabba; cdecde).
His metaphors were also of a limited kind. The first eight lines stanza (octave) was dedicated for the appreciation of the lady in almost set terms. After this formal recounting of “said beauties” – or sometimes the story of suffering of the speaker – the speaker goes on to propose and appeal to the lady to accept his long refused love.
The Petrarchan form was later used, and for a variety of subjects, by Milton, Wordsworth, Rossetti and other sonneteers, who sometimes made it technically easier in English by introducing a new pair of rhymes in the second four lines of the octave.
Many English poets wrote sonnets in its original classical form. But the most popular English sonneteer, William Shakespeare, changed and adapted (all three important elements of poetry in it) to the convenience of the English language and rhythm.
