Most office supply stores sell high-lighters. The idea is pretty good. You high-light important text in yellow or pink to make it easy to find again. So if you are reading a book or report, you simply high-light the important parts of the text.
Obviously this can help you find information more quickly in the future, but it isn’t really the most productive method. Instead of using a high-lighter use a black magic marker and simply cover up all the text that isn’t important. That way it won’t be around to distract you when you come back looking for the important stuff.
This is particularly helpful if you are working with legal contracts.