No matter how much you may think somebody is not doing something correctly try to restrain at all times from telling them how to do something.
The only person in class who should be giving instruction is your coach and / or anybody who he has told to assist in coaching that particular session.
I have been training Jiu Jitsu for nearly three years and have a pretty good grasp of most fundamentals now. Just last week whilst in class drilling knee escape from full mount I had my escape corrected by somebody who is a complete novice at BJJ and who had only taken two classes prior to becoming this fountain of knowledge. I smiled politely and continued to drill the way I have been shown to drill over the past couple of years.
I have seen blue and purple belt BJJ guys get a telling off from the black belt instructor for correcting somebody’s technique without being given permission to do so. What works for them now that they have a more solid game may not work for a beginner, that is why it is so important that the beginner learn the basic technique text book fashion, so to speak, that is with no refinements.
For example, the more advanced student may have a killer guillotine that they can always pull off when sparring, but it may be an adaptation that suits their paticular attributes rather than being the fundemental way your coach would teach you. There is certainly nothing wrong with adapting a technique to suit your attributes but that adaptation should not be passed on to beginners until they understand the basic motions and mechanics of the guillotine.
Fundamentals should be learned correctly from the outset, adaptations can come later once you understand the technique. If somebody other than your coach tries giving you advice on your technique, smile politely and carry on as you were.
