A precis is a summary. Precis writing is an exercise in compression. A precis is the gist of a passage expressed in as few words as possible. A precis should give all essential points so that anyone reading it will be able to understand the idea expressed in the original passage.
Note that precis writing is different from paraphrasing. In a paraphrase you should give all the details: you should not leave out any details. A paraphrase will be at least as long and sometimes longer than the original. A precis, on the other hand, must always be shorter than the original. It should express only the main theme that too as briefly as possible.
How long should a precis be?
There are no rigid rules regarding the length of a precis. But as a general rule, it should not contain more than a third of the total number of words in the original passage.
Uses of precis writing
Most people read carelessly and fail to fully comprehend the meaning of the passage. Precis writing forces them to pay attention to what they read because no one can write a summary of a passage unless they read it carefully. So summarizing teaches one to read with concentration.
Precis writing also improves your overall writing skills. It teaches you how to express your thoughts clearly, concisely and effectively.You learn to choose your words carefully and construct your sentences in a logical and concise manner.