Crouch a lot, it keeps you off radar until you're close. If you aren't very good then it's best not to rush around the map because your encounters will not be on your terms for the most part. Hang back and let enemies come towards you and hopefully you get the first shot off. Most gunfights are determined by who has the first shot and better aim. Learn the Maps! Most important thing period. Use weapons that you're comfortable with, stats don't matter in crucible so whatever you're best with at getting consistent headshots will serve you well. Find and remember heavy ammo spawn points. Do not grab heavy ammo until your team is either at the spawn point or you're sure no one else is coming and maybe an enemy is on the way to it. Special weapons seem to rule the crucible. Ammo is very abundant so a lot of people just run nothing but a shotgun or fusion rifle. It's annoying but if you're skilled with either then by all means you will have success spamming it