Don't Write The Way You Speak

The most common writing advice I hear (at least as far as style goes) is to "write the way you speak. The idea is that, by doing so, your language will be more natural and sound less stiff or stilted. As of now, I have to disagree with this advice. 

Written and spoken language are fundamentally different. They use different organs to receive (eyes and ears) and are processed in the brain differently. Because of this, they use different sentence structures and follow different grammatical rules.

Despite both being contemporary English, writing and speech are different languages. If you try to use one to do the other, it will probably come off poorly.

Learn the differences between writing and speaking. Sometimes the best way to do it is by watching speeches and reading articles. You can absorb a lot of style by just surrounding yourself with it. Once you've done that, you will readily notice when somebody does it wrong.