if you're building pivots manually, you can set the sort order and field in the layout options dialog (apologies if this isn't exactly correct - it's not something I use very often - but it'll get you started)
double click on the field header, then select advanced.
Set the sort order (descending?) and the field name (it will probably default to the 'active' column anyway).
you can force your pivot to refresh on open under the options dialog (or select TABLE OPTIONS from the pivot context menu) - last check box is refresh on open