The best ones I have seen are the ones by Accelerated Education (AE). Available on Amazon and AE tuition. We used those and DS ended up winning a writing competition and also won an academic scholarship. They take you right from the basics but it does require patience to work through all their books and steps.
We also used a book called Desciptosaurus which gives lots of ideas for descriptive writing in themes.
My ds reads a lot but unfortunately it doesn't help with his creative writing that much. We have found sustained practice to be the best approach, go through it together looking at how it can be improved. BBC Bitesize is a good place to start.