Just like in face-to-face conversation, there should be a natural flow. You should feel it as you “converse” with your client. Picture them, in front of you, listening attentively… interested in what you have to give to them.
Try to avoid jumps in the copy, or abrupt changes in the flow and direction. Use paragraphs that bridge thoughts, bringing the reader along with you. Otherwise you risk leaving them behind, losing them. A lot of times these cuts aren’t in the original piece, but come in later during the final editing, the slicing and dicing.
Often, reading a completed letter or piece out loud will reveal awkward spots of grammar… places where you aren’t coming across. Take whatever time necessary to work it and rework it. Read it aloud… does it read right, or do you stumble on your own words. All of the words you write aren’t golden. But the ones left behind better be!