My first local tournament with Tyranids. Tips needed

This saturday is my first tournament. It's local so it's competitiv but with fun vibe. I usually play Chaos space marines at home with my wife, but I see her Tyranids seem to have more variety, with CSM if they destroy your Possessed, you are doomed. Any general tips with Tyranids Combat Patrol? What Enchancement you think is better and what's the Best time to play Shadow in the warp? Thanks in advance.