"According to most studies, humanity's worst fear is public speaking. The next biggest is dying. Does that sound correct? That means to the typical person, if you go to a funeral, you're better off expired than delivering the eulogy." John Steinbeck, Novelist
If you are writing and speaking in public, successful communication begins and ends with the what -- the content. The how will come easier. If writing training and presentation skills training help you in gaining success (and you will have confidence because you'll be a trained pro) you'll have no worries writing or speaking in public.
To get there, aided by writing skills training, remember the three pillars of effective communication, whether written or spoken:
Writing exercises the mind. Compared to an unplanned conversation, writing -- whether a presentation to a group or a report for the boss or a sales pitch -- furnishes you the opportunity to show how smart you are.
Understand your audience and your readers. How much do they know already? Are they specialists? Do they want to be entertained or informed or persuaded? What do you want them to get from your speech?
Plan and revise and, when delivering presentation skills training, practice time and again. If you do not review your work with care before hitting the "send" button, or rehearse the details and delivery of your presentation, you risk looking sloppy and unprofessional. It's called QC (quality control), without which successful communication is nearly impossible.