Code for sorting by default for ascending order or descending order in Magento 1
Go to your themse’s local.xml and place the code
<catalog_category_default>
<reference name="product_list">
<action method="setDefaultDirection"><dir>desc</dir></action>
</reference>
</catalog_category_default>
<catalog_category_layered>
<reference name="product_list">
<action method="setDefaultDirection"><dir>desc</dir></action>
</reference>
</catalog_category_layered>