Use the following guidelines when you are summarizing your own or someone else's writing.
Read the entire original once (or twice if necessary) without making notes. You cannot write a summary of a text you don't fully understand. If some parts of the original are still not clear, go back and read them again. Some writers find it helpful to try to describe the key points in what they've just read. You can then check your understanding as you go through step 2.
Reread the original, underlining essential information as you go. Focus on the purpose statement (if there is one) and the topic sentences in each paragraph. Try to summarize each paragraph in a sentence.
Go through the original again, this time crossing out any underlined material that you realize is not essential.
Draft your summary in your own words. Include everything you're left with after step 3, even if you know there is too much. You can revise it later.
Now edit your own version for conciseness. Cross out any words that aren't doing any work. Wherever possible, merge related ideas into single, concise sentences.
Go back to the original and check that you have preserved the essential information without adding any new content.
Copyedit your summary. Check the clarity of your sentences and paragraphs. Use transitions ("as a result," "next," "however," etc.) as needed to make sure the ideas flow logically.