To optimize pivot tables, regularly refresh and clear old items from the pivot cache to prevent it from storing unnecessary data. In the PivotTable Options, under the Data tab, enable the 'Number of items to retain per field' option to 'None' to ensure that unused items are not kept in memory. Also, consider using the 'PivotTable and PivotChart Wizard' to share cache between multiple pivot tables when they use the same data source.