As with most things Drupal, setting up multisite on my shared hosting with Godaddy proved trickier than first thought. It's not a case of a lack of documentation, more an excess of it. There were mutiple tutorials on Drupal.org so to cut down on the confusion, here's what worked for me (Godaddy shared hosting).
1. Set up you main Drupal site as normal. In my case, you are looking at it. If you need help with that, you are nowhere near ready to read further!
2. Add a directory in /sites using the name of your second (or subsequent) site without www prefix so: