A sonnet is a verse form technique consisting of 14 lines with a fixed rhyme scheme. There are many different types of techniques in poetry writing

It must have of 14 lines and be written in iambic pentameter (duh-DUH-duh-DUH-duh-DUH-duh-DUH-duh-DUH).

The lines should rhyme like this.....

A,B,A,B,C,D,C,D,E,F,E,F,G,G

A rhymes with A, B rhymes with B, etc.

Here is an example of a sonnet written by william shakespeare in 1609, you can study a perfect poetry technique by one of the greatest writers.

Shall I compare thee to a summer’s day?
Thou art more lovely and more temperate:
Rough winds do shake the darling buds of May,
And summer’s lease hath all too short a date:
Sometime too hot the eye of heaven shines,
And often is his gold complexion dimm’d;
And every fair from fair sometime declines,
By chance or nature’s changing course untrimm’d;
But thy eternal summer shall not fade
Nor lose possession of that fair thou owest;
Nor shall Death brag thou wander’st in his shade,
When in eternal lines to time thou growest:
So long as men can breathe or eyes can see,
So long lives this and this gives life to thee.