Highlight using a highlighting marker or a writing instrument like a pen. If you are planning on selling back the book or if you are in a school district which recycles books from year to year, then you may want to use only pencil when marking. This way, after the class is over, you can simply erase the pencil markings before turning the book in or selling it.
Mark sections which you think will be on the test. For instance, it is usually a good idea to note new vocabulary words and new concepts. If you are in a particular type of school like law school, you may want to also highlight the issue, rule, analysis and conclusion of a case by writing these words near the appropriate part of the text.
Do not overmark the text. Read through the material once. Highlight the text on the second read through in order to avoid marking too many items. Stick with one highlighting color to avoid potential confusion later. Try to highlight no more than 1/3 of a page of text. If you think that actual highlighting of a text is distracting, then you may want to make marginal notes using a pen or pencil to mark important information you want to review later.
Highlight items which are set off in a group like a list of items or a chart. Use common sense. You do not need to mark every line of a large chart or list. You can "highlight" by making a large asterisk, or star, using your highlighter next to the list or chart.
Think critically about the information which you are highlighting. Carefully consider it before you accept it. This will help you to store the information more easily in long-term memory and perform well on tests.