Every 2 strokes on the right side. I have been doing this since I started on a swim team when I was 13 years old. I'm 35 now and still swimming that way.
I've tried bilateral breathing... but it was just too much effort. I swim fast doing what I do now... why spend effort and energy on improving it... when I need to spend that time on improving my running and cycling.
Good luck on finding what works best for you!
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"