I am a big fan of Clutch Chris, I’ve linked that video myself, in posts dealing with gnasher only plays. He is such a super nice guy (I’ve played with him)
I am enjoying working on getting “better”, I don’t have any great wisdom yet, but a few observations/things which allowed me to feel less like cannon fodder against good players 
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Recognize when you are at a disadvantage, and (unless there is no choice), back off. Pushing a player who is in cover and has right hand advantage? Nah, go around, if you can. If you have to push, use a smoke first…
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CQB gnasher combat is the hardest thing in this game to master, with the biggest skill jumps between skill levels (rank tiers?) You can be highly effective with lancer support fire even against much better players. Trying to gib much better players is gonna get you killed. A lot. Over and over. Put damage on the opponents with lancer and pistol, and then if you have to use the gnasher, shoot them from a distance! If you wait until they are in your face you lose the benefit of any damage you or team mates put on them already.
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Recognize when you are an easy victim of a “trick” shot (UpA, backA, etc) and move away!
I find most of the time I die it’s because I allowed the opponent to get into an advantage position, because I didn’t pay attention. And good players will exploit every advantage you offer them, every time.
