“You look so hot right now.”

This should be your go-to line, because you can use it in just about any situation—whether she’s wearing a ball gown or a bikini, says Carole Lieberman, M.D., a relationship expert and author of Bad Girls: Why Men Love Them & How Good Girls Can Learn Their Secrets. Saying this makes her feel desirable, and, as long as you’re being sincere, will come off as the ultimate compliment.