Hello :)
My answer would be, you should be constantly working on your style as you write. Whether that means cracking open the thesaurus or checking words in the dictionary- you should always be working on your style. If by correctness you mean punctuation and grammar, the best time to do that is after you have everything written. If you do it after, you’ll be able to nick-pick at every detail and improve whatever it is you’re writing.
Hope this helps >.