Posted on February 18, 2015 | Magento 1
Add the following snippet to your Namespace/Module/etc/config.xml file.
<?xml version="1.0"?>
<config>
...
<default>
<sectionname>
<groupname>
<fieldname>My Default Value</fieldname>
</groupname>
<anothergroupname>
<fieldname>My Default Value</fieldname>
<fieldname>My Default Value</fieldname>
</anothergroupname>
</sectionname>
</default>
...
</config>