No matter what you read, you always have some prior knowledge of the subject, even if only a very small amount. Help students use this prior knowledge to their advantage through a brainstorming activity. Ask students to read the title of the text they are about to read. Then have them brainstorm all the information they know about the title. This strategy will help students activate what they already know, knowledge they can draw upon as they read.
All reading should have a purpose, whether students are reading a textbook or fiction. Help students define what their purpose is in reading by forming a series of questions to keep in mind as they read. If they are reading a text on the American Revolution, for instance, they might focus their reading by asking what the principal cause of the Revolution was and who its main actors were. If reading a book of fiction, students might ask questions such as who the main character is, what the main plot points are and what the author is trying to say.
All books are written to be read in a specific order, but that order often reveals meaning in a sequence that makes the information difficult to remember. Teach students to manage their texts by reading the introduction and conclusion first. While this strategy might ruin any surprise that comes at the end of the text, it will help them go into their reading with a solid summary of the book's content. You can have students take notes on the intro and conclusion and write a short summary for themselves before they begin to read the body of the text.
It can help comprehension to look for other sources before beginning to read any text. Get students in the habit of spending a few minutes doing research on the topic before attacking a book. This can involve looking for other books in the library or doing a quick online search for a summary or introduction to the material. While much material online should not be used for formal research, it can be used as a quick and non-authoritative introduction to many topics.