I tried so many triangle counters that I came to the conclusion that none works for me.
So I just never leave one arm in and one arm out. That is best way for me.
Also like someone mentioned above, go combat base as soonest possible. Ie shove the knee in the middle
That makes totalPosture(Look straight or upwards), arm placement(two arms in or two arms out), Hand placement(Don't place your hands on their knee), and stand if needed.
Double under pass baby.
http://www.bjjee.com/videos/the-most-basic-but-most-powerful-pass-in-jiu-jitsu-by-keenan-cornelius/
That makes total sense, thanksPosture(Look straight or upwards), arm placement(two arms in or two arms out), Hand placement(Don't place your hands on their knee), and stand if needed.
Double under pass baby.
http://www.bjjee.com/videos/the-most-basic-but-most-powerful-pass-in-jiu-jitsu-by-keenan-cornelius/
That's definitely happened to me a few times, thanksPosture is the answer to almost everything in JJ. But I will add one thing, make sure you're not trying to pry open their closed guard with your elbows. It doesn't work after white belt and anyone with decent resistance to it can use that pressure to set up a triangle or break your posture...Which can then lead to triangles.
Everyone else has provided a lot of useful information. The only other thing to keep in mind is that if you can control their legs then you can't get caught in a triangle.