Actually, there is no one way to write a sonnet, or any other poem for that matter. A sonnet is a fourteen line poem. There are different rhyme schemes and structures for those fourteen lines. I will not discuss them here. This is simply a method I found useful in getting both the inspiration and technique to write a sonnet. It can probably be extended to any other verse form. It is one method among many. It takes time. If you wish you could probably figure out the rhyme schemes, or get them from a book and hash out a sonnet. But if you're looking to get some kind of inspiration to write something really worthwhile, this method may help. It has helped me.
I would suggest at the outset, finding a book of sonnets and simply reading them and enjoying them, for no other reason than your reading pleasure. Don't even sweat having to write one of these. Just like any rock band or rap artist usually grows up and spends their time enjoying a lot of other artists rocking or rapping, get into the world of the sonnet. Sometimes this immersion is enough to get your creative juices flowing. If so, go with the flow, write what you're inspired to write and forget about the rest of this article. If you seem to be blocked, and you really want to write something (Valentine's Day, a Birthday, an Anniversary, or the end of the semester, may be drawing near) try what follows.
Find a sonnet that really moves you, or that you find interesting, or one that has been assigned for reading, or that is in the form you wish to write, or your significant other's favorite, etc. There are many amazing sonnets out there. Shakespeare, Sir Philip Sidney, Elizabeth Barrett-Browning, Milton, Dante, all wrote a number of these poems. Other poets have written them on occasion.
Having found said sonnet by someone else, read it. Check out a references or words you don't understand, or strike you as odd. There may be mythological creatures, or flowers, or people mentioned. Look them up. Look for their pictures. Think about these , see if they remind you of anything in your life- even if it's just the sound of the word. Get a decent handle on the poem.
Now memorize the poem. Check out my Hub on How to Memorize a Poem. It can work fairly quickly with such a short form like a sonnet.
Once you have mechanically memorized the sonnet, recite it to yourself over and over as you go through the day. Think about the world, your friends, the person you want to write the poem for, your life in light of the poem. LET YOUR MIND RUN FREE with the sonnet as a sort of background chant. Follow any stream of consciousness type of thoughts that triggered by any words or lines or anything in the poem. At some point, at least this is what happens to me, something will jog in your mind and an idea, an approach and a single line may occur to to you. You may even have taken a rest from reciting the poem to yourself, be paying attention to something else, when a line occurs to you. This is why they call it inspiration, it just sort of happens.
Let the line come to you. Don't force it. Don't panic if it takes a day or two or even more of reciting and reflecting on the original sonnet.
Since you have been chanting the particular sonnet so to speak, the lines you think of may very well be in the style and meter of that particular sonnet.
But you have your first line! It is not necessarily going to be the first line of the poem you write. It might be a great ending line; it might make an excellent line in the middle of the poem; it might be a great hook to begin the poem with.
Now that you have a line, and perhaps an idea of where you want the poem to go, how should you proceed? Since you have been immersed in the one style your mind by this time will probably run in the same direction and you may quickly end up writing another line and another. Let it flow.
Mostly, I find mulling over that first line you have written, thinking about it what it means and thinking about rhyme words helps, but also to think about a line to follow up which doesn't rhyme but seems to follow the flow of the first line. Or another totally random line may occur to you. If it sounds good. and it contributes to your sense of the idea you have, keep it.
One mistake people make is called "rhyme forcing." You will hear it in a lot of bad hip hop, and the occasional clinker in really good rap. It is when someone throws a rhyme word in that really doesn't make sense to the song or poem and is only there because it rhymes. There are a number of ways to avoid this. One way is to use rhymes that aren't perfect. Near rhymes, like "rhymes" and "writes" or "rhymes" and "tomes" may be options, and not just "rhymes" "times" and "mimes." That opens up the number of words you can choose from.
Another way to avoid rhyme forcing is to let yourself be gently guided by the words which you have already written. Remember poetry is not like writing an essay or prose piece where you set yourself a topic and force everything toward that end. Sometimes a word, any word, but often the last word, in a line will suggest a rhyme or near rhyme. It might first seem to be totally useless because it has nothing to do with the subject you want to write about or what you want to say. But think about that word, the images it brings up, mull it around, it might lead you to think about other aspects of the world, or the person you are writing to. If it does, then although the direction of the poem may change, the rhyme will not be forced, it will contribute to the meaning of the final product and may even open up whole new vistas for you. You may learn something.
Let the music of the words guide you. If it is a choice between a line that technically fits into the form and one that really sounds good and contributes to whole poem go with it. If you are assigned to work within a strict rhyme scheme, well, then you may have to work it in some other way, divide it between two lines, or make it the seed of a new poem, or alas even discard it. Soemtimes in writing we hold on to lines we are attached to for too long and sometimes a poem falls into place when we just let go.
But it you are just set on writing a poem that works, that sounds good and says or reveals something then go with it. Hey what the heck. Writing a sonnet should be more like writing lyrics to a familiar melody or in the style of a song we like. Think of the original sonnet, and other sonnets you have read as just that, songs, not some kind of structure that you have to follow right done to smallest detail. Follow this method and you will have a melody in your head and a feel for the music to which you can write your own words. Good Luck and let me know how it works.