Read! Your writing skill will usually trail your reading proficiency.
If you mean business correspondence, find a nice book on professional communication (which may have to be adapted a little for modernity.)
Here’s the balance: less words more concise (unambiguous) meaning. Don’t meander. Use bullet point structure if you must. Try to supply necessary details you think others will require without round trips.
It’s okay to write an email, and come back in some time and reread it before sending. Self editing is like good hygiene!
