Here is 4...
1) Conciseness: unlike paraphrase, summary condenses information. The degree of density can vary: while you can summarize a two-hundred page book in fifty words, you can also summarize a twenty-five-page article in five hundred words. Both are summaries because both condense the material, although one condenses its material much more than the other does.
2) Accuracy: summaries should provide a clear and precise picture of the material, shorter length notwithstanding. In order to do this, you as the summary writer must understand the material thoroughly, and you must convey your understanding so that the reader gets an accurate picture as well.
3) Objectivity: summaries should only contain the original author’s viewpoint, not your own. You are reporting, not editorializing. Even a seemingly innocuous statement like “Smith helpfully points out that…” is subjective. You are not just presenting Smith’s point; you are also expressing your opinion that Smith’s point is helpful.
4) Think about the piece’s structure, and decide what the piece’s main point is, which statements are supporting points, and which are details.