If you have trouble doing this, the Hemingway App might help. http://www.hemingwayapp.com/
There are a lot of problems with the way people write. Some writers are too writerly, some are trapped in journalese or legalese, most are too vague. But better than any -ese is being able to communicate complex ideas to intelligent outsiders in a shared, common language.
To do that, you have to think a lot about what your main points are, how they connect, and what your readers will probably misunderstand. Then you address that. You answer questions before they are asked.
Sure, there are other ways to write. I like a good dose of purple prose, or 19th-century Russian fiction. But it probably doesn't belong in a memo.
In the end, you shouldn't write like you talk, because as many others have said here, talking is messy. The real trick is to write in a way that makes people think you're talking to them. The writer finds tricks that make it seem like she's talking, even though speech has been translated to the page. Then the reader can hear your voice, and there's nothing getting in the way.