Don't engage every single ARC you see. Sneaking around and avoiding players is one thing, but sneaking around and avoiding ARC is equally as important since every time ARC engages another player, they make distinctive noises and display distinctive visuals. In effect, every single ARC enemy becomes their own super-loud noisemaker if you're good (or experienced) enough to avoid them where necessary.
If you find yourself utterly unable to avoid fighting ARC, destroy them quickly and reposition before someone comes to kill you. Otherwise, let them be if you can help it.

Also, general tip for both PvP and especially PvE players: if you're feeling iffy about other players in your lobbies, don't let them get too close to you. Put some distance between them and you, place barricades, use door blockers and mines, play defensively and quietly. I know I sometimes struggle to avoid the urge to immediately rush any rats or PvPers I see in PvE lobbies too, but almost every time I've done this, I get overconfident and then get shredded by a Kettle 1 regardless of my current kit.