Your sentences need to have clear and logical breaks ("chunks"). Our thought groups in English are, on average, 3-4 words long. This is an average. You can also have longer groups or single word groups. At the end of a thought group we will have a split second pause or a change in tone. These short groups are also called "thought groups" because they tend to make sense when they stand alone - a bit like a short segment of a fuller thought (the full sentence). If you place a pause in the middle of one of these groups, it makes it very difficult for your audience to follow your train of thought.