It depends. Which version of SuiteCRM? I have a version 7 solution.
You just create a custom layout def and specify the sort order.
For example a subpanel in accounts:
custom/Extension/modules/Accounts/Ext/Layoutdefs/name of subpanel.php
I’m customizing the history subpanel, but you can do the same for any, here’s the relevant part of the code:
$layout_defs['Accounts']['subpanel_setup']['custom_activities'] = array(
'order' => 55,
'sort_order' => 'desc',
'sort_by' => 'date_due',
This will specify a default sort order.