If you're writing for a specific publication or a class assignment, you'll probably need to follow specific guidelines.
If there isn't a required format, you'll need to choose from one of two possible types of abstracts. The abstracts at Pub (National Institutes of Health database) are informational abstracts.
The researcher evaluates the paper and often compares it with other works on the same subject.
Critical abstracts are generally 400-500 words in length due to the additional interpretive commentary. A descriptive abstract indicates the type of information found in the work.
Then revise or add connecting phrases or words to make the narrative flow clearly and smoothly. "Criteria for Acceptable Abstracts: A Survey of Abstracters' Instructions." 14 (April 1963): 149-160; Abstracts. "Common Weaknesses in Traditional Abstracts in hte Social Sciences." 115 (January 2015 ): 41-47; Writing Report Abstracts. If the full-text is not available, go to the USC Libraries main page and enter the title of the article [NOT the title of the journal].
Note that statistical findings should be reported parenthetically [i.e., written in parentheses]. The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. If the Libraries have a subscription to the journal, the article should appear with a link to the full-text or to the journal publisher page where you can get the article.
How do you know when you have enough information in your abstract?
A simple rule-of-thumb is to imagine that you are another researcher doing a similar study.
Get to the point quickly and always use the past tense because you are reporting on a study that has been completed.
Abstracts should be formatted as a single paragraph in a block format and with no paragraph indentations.