Comment by RossBencina

An abstract and an introduction are two different things. For me, as a reader, the main role of the abstract is to help me to decide whether to even look at the rest of the paper, let alone read it. I want to know what is in the paper that I will not find in other papers that are competing for my time. Everything should be very clear: the context, the main research contributions and/or findings, novel aspects of the approach, limitations; plus any other information that in the author's view should motivate me to read the paper. Then if I do read the paper, there should not be any surprises: the content that the abstract promised should be present and, ideally, all of the valuable content in the paper should have been advertised in the abstract.

Different fields use different standard forms or styles for abstracts. If you have not already done so you can get a feel for this by looking at a random sample of the top 100 most-cited papers in your field (or your target conferences, journals, arxiv categories) and quickly compare to top 100 in a couple of disparate fields (e.g. biochemistry, economics, anthropology, mathematics).

Of course, there are good reasons to read a paper besides the quality and content of the abstract. Consequently, there are well known papers with non-standard abstracts. I recommend mastering the basics first.