If the essay you're summarizing is a long one, you may want to summarize subsections rather than the whole thing at once. You should still complete a reading of the full text before you start, but write each section separately.

When you have finished your linear reading, look back over the words and phrases that you highlighted, and re-read the comments you wrote in the margin. Then close the book and write down everything you can remember. If you can recall only isolated words and fragmented ideas, write them down anyhow, even if they're not coherent. Don't just write down what you remember immediately; sit for a few minutes and push yourself to remember everything you can.

Open your book and compare your summary with the passages that you highlighted and underlined, and compare it with the notes you took while you read. Look for important ideas that you misunderstood or omitted. Check everything you wrote to make sure it's accurate. But as you compare your summary with the text, do not write or revise anything.

Close the book again. Revise your summary, making it more accurate and complete.

Once again, open the book and check your summary against the text for accuracy and comprehensiveness. Also, check to make sure that you aren't duplicating the language of the source, copying its phrases and sentences exactly or with your own minor changes. If you find that you are copying too closely, you should revise and copy exactly, putting the source's language in quotation marks. But quote as little as possible; writing it in your own words will help you understand it, whereas having to use the source's phrasing is a signal that you don't understand a passage. If you find yourself having to quote often, it usually means that you still don't sufficiently understand what you are reading. At such times it's probably a good idea to consult with your instructor about the content of the piece.