I found this online doing a google search - much easier that describing it myself.

This shows them filleting a japanese yellowtail which has already been decapitated and gutted. You can fillet it the same way without decapitating or gutting it first if you want, but this will get you by. I personally don't have any pics of "how-to" and a verbal description would probably not be as helpful as this:
http://www.tsuji.ac.jp/hp/gihou/Basi...il_1/buri2.htm
In that tutorial they do not show that you should do the same thing to the other side to get your 2nd fillet. Here's how:
http://www.tsuji.ac.jp/hp/gihou/Basi...il_1/buri3.htm