As there is usually far more information available than you require, you need to make choices about what to read and how best to use it.

Consider  

•       Your purpose 

                    What do you intend to do with each piece of information?

                     Do you really need it?

                     Can you do without it?

•       What you already have

                   Brainstorm your knowledge of the subject  before you start your research, or make                    a list of the keywords you already know on the subject.   

•       Whether it is the best source 

                   Check to see if the source is reliable , up to date, written by experts in the field, and                      relevant to your needs.

•      Whether it is the best example    

              As you find more information, the latest information may be better  than what you                     have already collected. Keep evaluating which material is the most up to date and                         which is the best for your purposes.

•     How much you need 

                 Usually word limits are strict. Generally, you should't write more than a few lines or                   a paragraph on any one example. Bear this in mind when you take notes so that you                    do not record more than you need. this will save you a lot of time.