Adding new feature is always a fun, going through list of backlogs, talking to stake holders and trying to work out the priorities of user-stories in backlog. Its also challenging because you as product owner are always under pressure from sales who want to add feature that their customer is looking forward to, or their potential prospect would not sign a deal unless you add that one golden feather in your product.
To understand true priority most of us follow a release prioritization matrix, a document (MS Excel file mostly) that helps product owners to put weightage against various features (backlog items). This probably is a good way to do find out priorities of various feature requests.
While you work on your prioritization matrix, do all maths and talking, you must always remember the primary reasons for adding a new feature (points mentioned below), and unless new feature request falls in any one of the following primary categories just avoid its inclusion in your next release.
