The triangle choke is another basic choke that you will learn early in your BJJ journey. There are many small details that will make finishing the choke more effective. One of the most important details is to keep your opponent’s posture broken. One of the first things to do if you find yourself about to be triangled is to lift your head up and straighten your posture. So if you are executing this choke on someone, you need to keep their posture broken.
https://www.youtube.com/watch?v=oVvEQeasAxQ
Keenan Cornelius has some good details on perfecting the triangle choke in the two videos below. I personally find it hard to get opponents to put their hands on the mat and get the overhook, as Keenan discusses in the first video.
https://www.youtube.com/watch?v=80mqoNPw3Kohttps://www.youtube.com/watch?v=qyc9HdQz0Ps