The key to writing a summary of text, whether a journal article, novel, essay, speech,or any other form of writing, is to become familiar with the substance of that text. There is no shortcut for writing a good summary. The student must have a solid grasp of the item to be summarized. What are the arguments the author is making; who are the major characters in the case of works of fiction or of descriptive essays; how is the text structured (e.g., if it's a novel, is there a straightforward linear narrative, or did the author employ what is known as an epistolary format in which the story is told through letters, diary entries, etc., or does the narrative go back and forth in time); what are the author's thesis, when appropriate, and conclusions; and so on. The main point about a summary, however, is that it covers all of this ground concisely. A summary, in most cases, should be no more than a single page, although "executive summaries" of lengthy documents, such as of legal briefs and official reports, can extend for several pages, maybe up to ten in the case of particularly long documents.
If the student has a choice as to what kind of text to summarize, then he or she should select a work of literature or report in which the student has an interest, such as sports, history, music, etc., and read through it, highlighting specific passages to which the student wants to return later when preparing to draft the summary. Take notes on how the text is structured, on what argument the author is making, and on what the author concluded. If a novel is being summarized, what is the plot (in effect, what is the story about), who are the main characters, how does the story unfold, and how does it end.
The challenge in writing a summary, as noted, is brevity. The whole point of a summary is to inform prospective readers of the underlying text as to that text's substance. A summary, in other words, should provide all important information, but none of the extraneous information that may provide the bulk of the text. The reader should be able to read the summary and know what is in the underlying source material (e.g., the novel, report, essay, etc., being summarized) without having to spend hours reading the entire book, report, or essay.