The biggest trick is to start writing. Finding your voice, your style and learning acceptable grammar can come later.
If you’re a people-person, consider asking a sales call if you can tape-record your conversation with them. Then take that conversation and write out all those genius phrases and stories you use every day.
If you’re a short-hand guy. Write ideas and notes and concepts then have someone take the whole mess and spend a day trying to organize it into a few paragraphs.
If you’re someone who is shy chances are you’re already a good writer, but if some bad English teachers have gotten you down consider this: You don’t need an English major to be a writer, all you have to be is yourself.
In a day and age where prospects and consumers crave humanity more than ever, your voice your genuine nature shines out more when you’re NOT especially well polished or poignant with vocabulary.
Run your work by a trusted few people who are both good readers, and people who are not going to simply rip you to emotional shreds. They need to be able to critique helpfully, but also not be negative or down-putting.
I encourage you, beg you, to start writing. Write often, write a lot. The more you write the better and more confident your style will become.