1) People are not Google search engine spiders. Write online copy like you're writing to a friend - one friend at a time, not a room full of strangers (or search bots). Speak human.
2) Your customers simply don't care as much about your company as you do. They're not as technically knowledgeable as you. They don't live and breathe what you're selling. They want what you're selling, they just aren't going to be invested in it like you are. Talk to them, don't talk to yourself.
3) Show them, don't just tell them. Nobody takes a braggart seriously. But we do listen to testimonials, reviews, demonstrations, success stories and results.
4) You're the icebreaker at a party. Unless you're a stand-up comic, your monologues are going to get yawns (at best). Be a conversation starter. Your copywriting should spark a flame. Stoke the fire. Light up the room with your insights. Then get out of the way. Let the conversation build a life of its own.
Social media. Online advertising. Blogs. Posts. Email blasts. Content is king, but how you write that content is even more powerful.