It can be challenging to get your voice right, especially at first. Glad you asked here in the forums because other SBIers have been challenged by the same thing. Have you looked through the SBI! Tips articles about how to write? They cover topics like mindset, connection, trust, power words, etc. You can find them here...http://sbitips.sitesell.com/
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Creating Content › How to Write
A tip that really helped me was to create a persona, write out a description of him/her and then sit at a table across from an empty chair and write as if I was talking to that persona. It's a little awkward at first but after some practice, you start writing like you speak which makes future writing much easier since you can just be yourself.
Hope this helps a little!