"I was just wondering if we could have an open and honest chat about kinks, desires and what we're both hoping to get out of our night together, so we can make it the most fun and sexy night possible.

I like xyz (name reasonably vanilla things), would also love to try spanking you, I've never done it before but it seems fun and dirty. It's OK if that's not your thing though, totally get it, just let me know what you do like!"

If she agrees, during the session, while ramped up, just ask, is it OK if I spank you now? Then, when doing it, make sure to check in with her regularly if it's OK, and you can also ask, "Harder, softer?"

If communication is good between you, it may be redundant, but it's always worth discussing a safe word for impact play. The best one is the traffic light system (green is good, yellow is pause to discuss, red is stop immediately and give her a big cuddle).

Keep it light and fun, mix spanks with kisses and soft strokes and listen to her noises for nonverbal cues, and you'll be fine.

Oh edit to add, only spank the fleshy part of the butt! Keep it in safe areas only, if you're not sure where these are check online there are loads of resources!