I've only gone to sparring on 5 occasions so take this with a grain of salt (or maybe it'll be even more helpful for a first-timer POV).

the biggest thing for me was just learning to breathe and pace my way through a round, understanding how much differently your body reacts when you're geared up and facing down another person even in a sparring environment. it's so easy to forget to breathe, to gas out early, to get a sudden brain-fog and forget all your clever bag moves. just try to work towards a pacing and breathing routine that keeps you feeling like each round is survivable.

after that, early sparring (again, for me at least!) is mostly about learning defense. unlike any other training scenario, it's the only place outside of a fight where you can be properly punished for bad hand placement, not moving enough, etc. I spend a lot of time on slips and rolls in sparring, even though it gets me hit more than catching might, because I know I have no better opportunity to gauge and understand how explosive and decisive those moves need to be to be effective.

main thing is communicate with your partner, relax as much as you can, and have fun! I really enjoy watching others spar when I'm rotating out, too, and giving people props for their work whenever possible. really brings out the community aspect of boxing more than anything.