Skill comes with time really.
Learn to wield a magnum, learn map layouts and sight lines. Figure out how to traverse maps with Spartan abilities.
Generally the enemy team will spawn across the map from where your team is located. That helps.
Its all time, just play, practice you’ll get better.
If I had to give one tip:
Stay alive, don’t chase someone down for a kill. Readjust for every scenario.
I agree with everything you've said.
What do you mean by "don't chase someone down for a kill"?
That someone you let get away, usually sneaks back to kill you. and also, if you chase them down, they may be spring a trap for you and end up killing you as well.
Some other times, I've tried sprinting far away from the point of encounter - but they chased me down and killed me!! :(