Im awful at crucible

Use a play-style that is unique to you. For example, I main the empyrean bellicose, with flashbangs, and a preydyth's timepiece/hand cannon for sweats. Using a playstyle that is unique to yourself will help strengthen that play style's pros and cons. You'll automatically learn to be more accustom to your downfalls, and hence forth, die less. Rumble is the best place to practice. Rumble promotes primary usage. Find a good primary, and use it in every engagement, only use your sniper when to get a nice double, kill a rushing shotgunner, or for long range. Don't use a shotgun. Last tip, find a way to play with the best players in destiny. I've played with nearly all of the top players on my system when I was starting, from then, i've grown into one of them. It's either adapt, or fail, and your brain does not like to fail.