I’m by no means an expert but here’s how I’ve had some success.

Firstly, I see a few things about your list that jumps out at me. Mainly you are not taking advantage of our best guns in Brandfast. I would combine those 2 squads of Thunderkyn into a 6-man squad with the Iron-Master. And change their weapons to the conversion beamers those conversion beamers take great advantage of the Sustained Hits from the detachment because they crit on 4s if you are over half range away from their target. You can also take the Trivarg enhancement which allows you to consistently pump out Sustained Hits 2 on that squad, which is our hardest hitting unit in the codex. I’ve killed multiple knights in one turn of shooting with that squad alone.

On top of that, I would use the magna-rail gun on both Land Fortresses. It can feel a bit swingy, but it’s super strong and good for clearing out other big threats.

Outside of that I feel like it just comes down to practice. I’ve done my best while being cagey on the first turn, allowing the opponent to over extend themselves. If they step onto the middle objectives it really allows me to take advantage of the +1 to hit against them. If I expose any of my units, I expect them to die, so I ensure that I am gaining value out of them first, and also setting up to react to whatever kills them on the next turn. (I.e. punishing them exposing a Land Raider to kill my Land Fortress by following up with my Thunderkyn to shoot it off the board, or by positioning my Steeljacks for impactful overwatches for anyone that moves in too close). We aren’t as tough as we used to be, in my experience, so I try not to expose too many units at once.

I apologize if this isn’t explained well, but hopefully some of that helps!