For questions that ask you to predict what the author may want to say next or what the topic of the next paragraph may be, look for logical clues in the provided passage.
For example, if a reading passage focuses on the enlightenment period of the 1500s, and three examples of notable people are provided in three separate paragraphs, then it's a good chance that the next paragraph should be a summary or conclusion paragraph. Likewise, if an introductory paragraph of a reading passage elucidates on the pros and cons of an argument, and paragraphs two, three, and four focus on the pros of the argument, then it's logical to assume that the next paragraph or several paragraphs will focus on the cons.
The reading passages that you are provided generally follow standard essay styles, and thus include an introduction, supporting evidence, and a conclusion, and so use this fact to your advantage when answering "what will the author say next" type of questions.
When confronted with a reading passage question that asks you to predict what the next paragraph or sentence may be about, look for key words and focus on the style and degree of development of the provided reading passage. Keep special notice of the structure of the reading passage and how arguments, examples, etc. are constructed logically.