First ... you have to capture the potential buyer's attention. Nothing will come of your brochure, your website, your advertisement unless you get the prospect's attention. Good strong headlines and well-designed graphics do this.
Second ... you have to get them to read beyond the headline and for this you must create some interestin your product or service. For this you need good copy writing. Good marketing copy writing does not focus on you or your business or your product. It focuses on what benefit you can provide to your buyer.
Third ... the person reading your marketing piece has to do something. They have to take some action. Unless the reader becomes a customer, your marketing piece has failed no matter how well-designed or well-written.