Should you write the way you speak? The answer to this varies depending on who you ask. Effective communication is an important part of writing. The reader must be able to understand what you are saying. Not everyone use proper grammar when speaking. This is usually not acceptable in writing. However it is also important not to have writing that comes off too formal or stiff. Don’t fill your writing with a lot of complex words when simpler words could convey the same message. A few is fine but don’t over do it. Your reader wants to keep turning the pages, not constantly consulting a dictionary to understand what you are saying. Good luck and happy writing.