An explicit preview would be phrased much like the object of the document: "This section first . Do not make readers guess: Make sure the paragraph's first sentence gives them a clear idea of what the entire paragraph is about.
If you feel you cannot or need not do more than list items, consider using a table or perhaps a schematic diagram rather than a paragraph of text.
Start by stating the actual situation (what we have) as a direct continuation of the context.
If you feel you must explain recent achievements in much detail — say, in more than one or two paragraphs — consider moving the details to a section titled State of the art (or something similar) after the Introduction, but do provide a brief idea of the actual situation in the Introduction. Emphasize the contrast between the actual and desired situations with such words as but, however, or unfortunately.
You may also want to anchor your context in space (either geographically or within a given research field).
Convey the need for the work as an opposition between actual and desired situations.
One elegant way to express the desired part of the need is to combine it with the task in a single sentence.
This sentence expresses first the objective, then the action undertaken to reach this objective, thus creating a strong and elegant connection between need and task.
To reach their goal, papers must aim to inform, not impress.
They must be highly readable — that is, clear, accurate, and concise.