Write like you talk
If you've ever read a verbatim transcript of an interview or conversation, you'll know that actual speech is anything but clear. When talking off the cuff, even the most clear minded people tend to ramble, um and ahh, double back, talk across each other, and jump between points and subjects.When listening to someone in person, our brains seem to edit what they say on the fly to make it comprehendible, focusing on the important bits and forgetting the rest. When it's presented in written form, such as in a newspaper or magazine article, a skilled journalist has usually done the editing for us.This means that what we consider a “conversational” tone in written language is not a representation of natural communication so much as an idealised version of it. That doesn't mean it isn't useful to strive for it, particularly in business and academic writing that otherwise tends towards the turgid, but it isn't as simple as telling people to “write how you talk”.  Writing conversational prose that achieves clarity  whilst not being oversimplified, patronising or banal requires practice and skill.I also think, conversely, that while a conversational tone can improve formal writing about complex topics, the reverse can be true. It's possible to enliven mundane topics by being less direct and more playful with language.