Im a newbie please help me get good

hey im a begginer to the game, i started playing THE game last week and gotta say I already love It, i never played any hero shooters before and gotta say this is a great game, im loving it so far, i play It on Xbox, i wanted some tips on How to get good cause i enter a match and get killed in 5 seconds, so far my mains are iron Man, the punisher and Groot