This might be a silly question about PvP, but how do I die less?
If I could figure that out, that would solve a lot of problems.
What's your class and sub-class?
Apart from that, I can give some general advice. I'm actually in the process of helping a friend get used to playing in The Crucible.
From my experience, when you first start out the most jarring thing is learning the maps and its choke points. When the match starts, people tend to flock to certain areas and knowing how to get to these areas before they do, or flank them is pretty helpful.
While you're learning, I might suggest following another player or two around as support. Help in fire fights, and clean up the mess if he dies but doesn't eliminate his opponent. Power in numbers and all that.
Starting out, I would use the gun with which you're most comfortable. If you're trying to play into the meta and you're not used to those weapons, it'll affect your gameplay significantly. Once you're used to the maps, feel free to experiment.