预=pre- 习=study , so it can only be used in things that you need to learn. If you use 准备课文, that suggests you are the teacher. You prepare the text so that you can teach. More common way to say that is 备课. 准备+sth. suggests the subject is the provider.

预习：students get-prepared before a lesson so that they can learn more efficiently during the class. eg.read the text , look up new words before next class 准备 is used in many different situations. 1. 准备 means "Prepare"： eg. 我在准备一个演讲（I am preparing for a speech） 我在准备一个考试（I am preparing for a test） 2. 准备 means "be going to do" 我准备去罗马旅游（I am going to make a trip to Rome. ） I prepared some questions. 我准备了一些问题. (correct) I prepared this text 我准备了这个课文.(correct) 我预习了这个课文（I previewed the text）

準備 can be use at many aspect. 預習 only use at study. It means "read the textbook before teacher teaches it". I prepared some questions. (o) 我准备了一些问题. I prepared this text (o) 我预习了这个课文 準備 for example Are you ready? 你準備好了嗎？

I hope this can help you understand: 准备：prepare/plan 预习：预pre, 习study

预习 only means you prepare something for the coming class as a student. For example, if you want to say, I prepared these words. If you indicate that it's for the coming class, words are fro the textbook, then you will say 我预习了这些单词。