Tips on getting better?

I keep on getting bodied in quickplay. I feel like I relied way too much on bullet magnetism in older games. Would like some tips on getting better.

I mostly lose gun fights when they get the jump on me or in a sidekick duel. I do fine with the battle rifle since it’s been my favorite gun since Halo 2 and I can consistently win with that gun, but besides that I just get absolutely stomped.

I also never get kills with the Commando. Any tips with that gun since it seems to be the transition gun between AR and BR?

And lastly, any teamwork tips with randos outside of just talking to them? Like, let’s say you don’t have voice chat and are in the middle of a gun fight or just don’t want to “talk” talk with them.

Thanks for the help.