Do you mean handwriting or writing as in compositions of words?
Anyway, the best way to improve your writing is to read like crazy. Read read read. Read the newspaper, read poems, read stories. Read magazines and books. Anytime you have any type of curiosity about anything,, look it up on the internet and read about it. Also read reviews about movies and songs. There a lot of variance in reviews and you get to see a lot of different writing styles.
As far as a method of writing that proves the be very successful ...you want your first two sentences to get attention. You want the first sentence to hook them in, then your second sentence to say why the first sentence is true.
Then spend the rest of the article or composition proving it, then wrap it up in the last paragraph by reviewing the whole thing. The best way to make sure you're improving is to have friends or relatives read It and offer suggestions. Remember it may take several drafts to get it right but don't get discouraged.
Good luck and if you have any more questions feel free to ask me.