Have you ever read an email, proposal, or contract, and have no idea what the writer is talking about? As an attorney, this happens to me all the time, which has taught me the value of speaking and writing in plain English.
Plain English basically means K.I.S.S.—Keep it simple, stupid. Speak and write in words that are clear and concise. Avoid overly drawn out sentences, paragraphs, wordy phrases, etc. Make your point and make your point quickly.
I have been guilty of writing too much legalese at times, but I do my best to speak and write in plain English. Do you?