You could always channel Bella Auror Lestrange and her demeanour, but since that would be something of an insurmountable task for anyone, maybe not.

They know you have power, and there are subtle ways that you can let them know that you know you have power, too. Without using words or taking points or anything else. Wear your hair back to make the colour less noticeable, if it concerns you. Somber clothing choices. Speak slowly, with measured tones and pauses - it makes them keep listening. Keep your body relaxed, so they know you're not intimidated. Always, always make eye contact.

But you're good with people. You have good instincts. I think it will go better than you think.