If your app description is too long and it is not interesting, then user gets bored.
Explain the features & important points of the app, so that when a user reads it, he/she observe that it is valuable or very unique app as compared to others.
Poor app description doesn’t tell user what the app really does. if we don’t know what the app is for, why we download it. so always mention that, what the app actually does.
Before downloading app, everyone views the reviews & rating of that app, whether rest of the users loved it or not, so start with your best reviews.