Legend: Caustic Ultimate

Passive ability: Nox Vision - allows you to see enemies through gas.

You want to try and use the gas traps and gas grenade in close quarters where you can see the enemies through the gas while their movement is hindered.

Use your preferred close quarters weapons to help you in this task. EVA-8 is nice for Caustic etc.

https://www.ea.com/en-gb/games/apex-legends/about/characters/caustic

If you're trying to lob nades and traps in the open you will want to think about how you can use the space around you to your advantage. Place traps behind cover so they can't be shot and in bushes where they can't be seen. Stand close to them and even shoot them before the enemies get to you to activate them. Lob a gas nade on your own position and get blasting.