How to set default value of a new form's list lookup control?

To set a value to lookup control: 

use 'LookupId;#LookupValue' like below.

NWF$(document).ready(function()
{
   NWF$('#'+ddlLookup).val('5;#Servicing');
});

For Change Event:

you can change event
NWF$('#'+ddlLookup).change(function()
{
   var lookupVal = NWF.RuntimeFunctions.parseLookup(NWF$('#'+ddlLookup).val(),true);
   if(lookupVal == 'Servicing')
   {
      alert('Servicing');
   }
});