There's really not much more to say, is there?
Except:
1) Tilt the beret.
2) Have some hair joojing out the sides, as here, to soften the angles.
3) Wear a strong-hued, matte lipstick.
4) Smolder.
(photo of Lauren Bacall from Wes Clark's superb film noir website, Web Noir, thank you Wes!)