Important points to remember:

Keep the essay question beside you while you read; this should keep you focussed.

Always write down the bibliographic details; time is wasted when you have to go and find a book again just to get the page number or place of publication.

Make sure you have identified the relevant themes and issues before you start taking notes.

Always read with the question in mind. If the information is not helping to directly answer the question, then it is probably irrelevant.

Always skim read an article before taking notes so that you know exactly which parts of the text are relevant to your question. If you take notes on a first reading you may run the risk of noting down irrelevant material.