I'm playing the defendant in mock trial at school and the hearings start tomorrow, any tips?

The defendant is testifying in this case, therefore I'm subject to. direct and cross examination. What should ('nt) I say during the hearings?

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The plaintiff got into a car accident and her partner were driving home from a bar after throwing a birthday party for her partner. They turned sharply and caused a rollover accident. The plaintiff survived but their partner died in the accident. The brake line was corroded and frayed and the cop said at one point while tailing the plaintiff's vehicle, the car visibly slowed down but then didn't slow down anymore even though the brake lights came on. BAC was.06% several hours after the accident
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She was below the legal limit then. And the defendant (the plaintiff's ex) is being charged with second degree murder and attempted second degree murder. He admitted to being on the scene, hoping to extend an olive branch. However, he decided against it and was only there for around two minutes before leaving to finish cleaning up at his family's auto shop. The cop found a brake line cutter in the shop, but didn't bother to test the liquid surrounding it and assumed it was brake fluid.
I'm playing the defendant in mock trial at school and the hearings start tomorrow, any tips?
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