For an empirical piece of research a good abstract contains all of the core components of your paper. From hypothesis/research question/theoretical framework to your method, design, procedure, main findings, and main implication. It must contain each of those elements. Best to keep it within 150 words and one sentence for each of the elements. Write your abstract once your paper is written. Look to the top journals in your field of research, then choose some abstracts as templates and work from there.
It should summarize the problem the study addresses, the methodology (very briefly) and indicate the findings. It should at least hint at the discussion, also.
In my book, a well-written abstract should be a gist of the whole paper. It should contain the introduction, review of the literature, methodology, data analysis, discussion and conclusion. Wrting even a line could be enough for each section.
It must include a summary of all the main points. Beginning with a definition to the phenomena under investigation then the data collection procedures and finally the results.
The summary should include a presentation of the most important results and how they are sometimes obtained, the methods of work, the purpose of the subject, and the main conclusions reached
I suggest abstracts need to be succinct and written with clarity. Give the aims and objectives and conclusions.. Avoid at this stage too much detail. Readers first want to see if the paper is of interest to them. Then they proceed to read the full text perhaps starting with the conclusions. Avoid lots of acronyms.
to me a well written abstract gives a brief narrative of the research and sums up the journey from "what is the research about, why is it important (context)" to a short summary of results.