My personal recipe for an effective abstract (1 sentence each, ideally):

1. Big motivating question
2. Goal of this paper
3. Methodology
4. Central result
5. Broader (but concretely specified) implications of results

To be clear, it's hard to write each of those sentences well! https://twitter.com/JoshuaSGoodman/status/1340985573998284802

Deviation from this recipe is fine, so long as it stays within a sentence-related budget constraint.

If this motivation's obvious, skip it and give yourself two sentences for the results.

But treat each sentence and word as precious and make them work as hard as possible.

Here's an abstract of ours that I'm particularly proud of. Note that it's only four sentences, as it combines the goal and methodology sentences (#2 and #3).

https://www.aeaweb.org/articles?id=10.1257/pol.20170503

Another way to frame this recipe for an abstract:

1. Why should you care?
2. What are we trying to do?
3. How do we do it?
4. What do we find?
5. What does this mean? (So what?)

Titles are arguably more important than abstracts, but I don't have a recipe. I've done:

Short - "Heat and Learning"

Long - "Inequality in Household Adaptation to Schooling Shocks: Covid-Induced Online Learning Engagement in Real Time"

Silly - "The Wages of Sinistrality"

What I do know is that my most undercited article (measured by ratio of citations to quality) is one where the title we settled on is, in retrospect, not as informative as it could be.

You wouldn't know from the title that this district expanded access and eliminated racial gaps in math placement between students of similar baseline skill, by doing placement based on prior test scores.

"Objective Course Placement and College Readiness" https://drive.google.com/file/d/1yibG52ncqKNYVFwrx_WPiQSZtMOgV6Mm/view