First steps to writing a summary
1. As you read, underline all the important points and and all the important evidence. For example, you could look for all the topic sentences. Words that are repeated several times are likely to be keywords. Transition words can help understanding of the overall structure of a passage.
2. List or cluster the main idea of the whole piece, the main supporting ideas, and the main evidence for each idea. Use of the same keywords or technical expressions is probably unavoidable. However, be careful to express the ideas in your own way, using your own vocabulary and expressions as much as possible, rather than copying or just rearranging. Do not include too much detail.