How to Write a Sonnet

The sonnets of Shakespeare and Spenser are almost identical in structure, 3 quatrains of four lines concluded with a rhyming couplet.
It would not take a genius to surmise that sonnets thus consist of 14 lines. It is up to you, but I would recommend you also follow the rhyme structure of Shakespeare, as it is simpler.

Shakespeare rhymes line 1 with line 3 and line two with line four. We would refer to this as an abab,cdcd,efef,gg rhyming pattern.
Spenser uses an infused rhyming pattern, abab,bcbc,cdcd,ee.
Please ask for further explanation if that confuses you.

So a summary of what we have so far, 14 lines, divided into three four line quatrains and a rhyming couplet.

Both Shakespeare and Spenser formed their poems of Iambic Pentameter, for an explanation of which I would direct you to this thread.

What is a poem without a theme? The aim of a sonnet is not random garbage put together nicely, it is a question, or a pondering. In quatrain 3 this thought should be developed and in the conclusive couplet, it should be? You guessed it, concluded.
I’m not a master poet, but If I may link to my own writing just one
more time? This is a sonnet called Swirling Imaginations Hath. Note how the theme shifts in quatrain three and then concludes in the couplet. I’ve used Shakespeare’s rhyme sequence.

So in essence that is all you really need to know of sonnets, for examples of sonnets google is a perfect source, there are a million and one Shakespeare adoration sites out there for you to browse.