Girls, use your mouth

Statistically, the mouth is the facial feature considered to be the most sexually attractive by men.

The reason why scientists believe this is the case is that when Man started walking upright (and I am referring to the standing posture, don't get me wrong :P), the females of the Human species no longer had their genitals exposed and, as such, could no longer exhibit their sexual excitement by the redness of their vaginal lips.
This would have caused the male some problems in recognising the female heat season, which is not surprising when we consider how mixed up a male can be about women's excitement without a subtle sign such as red vaginal lips on their face.

The solution that evolution seems to have found was to give more relevance to the mouth lips that, unlike all other primates are, in the Human species, externalised and quite prominent. For curiosity sake, the same seems to be the case with the pair ass/boobs, which explains why unlike all other mammals Human females have big and voluminous boobs even when not milking.

So girls, don't forget your both. Show it off with lipstick and all the other 327 ninja techniques you have and that men don't even dare to know and just accept as they are.

And also don't forget the most sexy, appealing and effective way to attract any man with your mouth that does without all other extras, even naturally sexy lips:

Smile!