This time we’ll talk about abstracts. The first two sentences are arguably the most important. You need to quickly convey the purpose of your research as well as the context.
Here’s the first sentence in an abstract from a recent paper in Nature:
Although p53-mediated cell-cycle arrest, senescence and apoptosis serve as critical barriers to cancer development, emerging evidence suggests that the metabolic activities of p53 are also important.
The authors clearly set up the context of their research. First they list the typical actions of p53, but then they mention new research that points at other activities. In the second sentence of their abstract they concisely state how they explored these metabolic activities.
This lets the reader know right at the beginning of the abstract what their research builds on as well as what it accomplishes.