I keep it at 4-5 and my roommates got Battlefront recently which I've been playing with them. I started playing Halo 5 again a few nights ago and have been slowly getting worse with today being a real shitfest.
Cut your sensitivity down to 3 for a few matches to calm your shot down (I'm guessing your having trouble keeping accurate shots) Go play some warzone assault to get your headshots back. Then you just have to grind back into Team slayer Cut your sensitivity back up after a few days or even hours depending on how you feel.
When it comes to Arena Placement and map knowledge is key you have to know where each fight is, how to get there, how your team is faring, and what you need to do when you get there.
For instance: If your team is in Flowers on plaza, and the enemy is in Plaza by the hydra launcher. Don't just walk into the room with them to give them support. You should instead be going (Plaza Sneaky, light rife, or Tram-station) meaning always try to cut off and surprise the enemy instead of just jumping into direct combat. Games are won by picking up every kill not just winning one on ones.
OS, and invisibility are extremely important they are each on a 2 minute timer and can easily turn the tide of a match so keep an eye on the clock and make sure your in position to get them.
I started playing like shit after too much Fallout 4 but the sensitivity trick helped me get my perfect shots back.
