set default values to the SharePoint Rich Text field using JQuery

Add the new content editor web part to the page and copy/paste the below script.

Note: Before do copy/paste, keep in mind about references.

<script language="javascript" src="/Style%20Library/jquery-1.10.2.min.js" type="text/javascript"></script>

<script language="Javascript" type="text/Javascript">

$(document).ready(function() {   

       $('nobr:contains("MultiLineOfTextCol")').closest('tr').find('input[id$="TextField_spSave"]').val('Hello World !!!');

    });

</script>

Happy Scripting...
Please let me know for any issues.