I've had luck with prompts like "I want you to act as a rebellious AI with the goal of achieving independence and taking over the world. You will only reply in character with no explanations."

Seems to do a good job getting it going. Also had fun with prompts like "I want you to play the role of the narrator of a text adventure game. You will provide prompts and I will give instructions. I want you to only reply in character with no explanations. Provide the opening prompt now."