Some of the important best practices for designing filters for faceted search results are:

• Decide on your filter value-selection paradigm—either drill-down or parallel selection
• Provide an obvious and consistent way to undo filter selection
• Always make all filters easily available
• At every step in the search workflow, display only filter values that correspond to the available items, or inventory
• Provide filter values that encompass all items, or the complete inventory

Best Practices for Designing Faceted Search Filters