A precise- means a summary. Precise writing is therefore a summary or gist of the subject matter comprising of the main theme, expressed in as few words as possible.
Precise writing is an exercise in compression. It contains the lucid, succinct and essential points of the subject matter as briefly, precisely and to the point in a concise manner. Anyone reading it must be able to understand the main points and the general effect of the passage or the subject matter summarized.
Styles of different writers may vary. Some are concise some diffuse, so no rule may be laid down for the length of a précis. However, a precise may never be more than one third of the number of words in a passage.