Sonnets are traditionally written in iambic pentameter, but don't strictly have to be. Nor do they have to conform to a strict rhyme scheme. But, like so many of these forms, it really does help to learn to do it 'properly' first, before you free yourself up to be more experimental.
So; fourteen lines, divided into three quattrains and a couplet, with a simple rhyming scheme, and all in iambic pentameter. I write dozens and dozens of the things. They're not too long, not too short, and surprisingly easy to write once you've done a few. Here's one I wrote on a very hot, sunny day last summer:
It’s too hot today
My bones are soft and seep between the cracks
Of burning wood where helplessly I sit
And grip the edge with fingers; can’t relax
While braced to stop this meltdown; bit by bit
I’m dripping through the slats with oozing pain
As fizzling heat releases from my flesh
The meaty smell of blood that from a vein
Comes throbbing out and spurts with strength afresh
Each time I move. Evaporation’s slow
But can’t be stopped. I sizzle, bleed and see
Myself like molten magma, and I know
I’ll soon expire if not revived by tea.
At half past two I go and make a brew
Relieved I wasn’t really turned to goo.