Lost a casual 500pt game against Tyranids - how to score?

Hi all, I played 2 small 500pt games against Tyranids and got absolutely crushed. I was able to score less than half of the points of my opponent! I am looking to improve with Drukhari, do you have any tips?

Regarding the game: 1) my list: venom w/ gun kabs, kabs+court+archon, mandrakes, reavers 2) opponent: screamerkiller, psychophage, neurotyrant + gants, 10 termagants 3) table 44x30 4) 5 objective markers, we played with leviathan secondaries

I deployed in cover and focused on secondaries, but he just pushed the monsters forward until I had nowhere to hide. I was able to take ~10 wounds total off of the monsters, but didn't manage to kill a single one. Thanks for any insights!