Makeup is key when it comes to recreating classic pinup style, and knowing how to get glamour girl lips will take you far. Wearing red lipstick is certainly more maintenance than wearing a barely-there lip color, but the feeling of confidence you get with a perfect pout is well worth a few more peeks in a mirror. (Note: I'll be recommending several products in this post, but I'm not paid in any way to do this. No kickbacks for me.)
Before you get started, you should have smooth lips. I have a terrible habit of biting my lips, especially in cold weather when they get chapped, but I've recently started using Lipscription from Benefit. They give you one tube of lip buff which takes off all the dead skin, and another of lip balm. I use both right before I go to bed a few nights a week, and the result is like a ribbon of satin on your mouth.
Next, you need to pick a color. I'm not very adept at seeing two colors and determining which one has more blue undertones and which has more brown overtones; I just know what I like. I'm quite pale, and when I was looking for my perfect red lipstick I found that the right red can make the difference between looking healthy and looking like a crypt-keeper. If you're like me, pay special attention that your red lips don't wash out the rest of your face. As I've mentioned in a previous post, my favorite lipstick is by Besame Cosmetics, due in part to their color selection. Their shades in Red Velvet and Cherry Red seem to be universally flattering. I tend to wear Red Velvet to work, and Cherry Red for the evening, as the Red Velvet is just a little more muted. Another thing to note in choosing a lip color is the texture. Classic pinup lips tend to have more matte than shine. If you want a bit of shine, smooth just a bit of gloss over your matte color, but in general you'll want to stay away from any all-over lip color with a Vaseline sheen.
Once you've found the right shade, you need a liner. A lip liner will define your lips and help your lipstick stay in place. I choose a relatively neutral red, as I find the neutral to be the most versatile. Another thing you can do to achieve a distinct line is bled your foundation just around the edges of your lips before you line them.
Your final task is to pick the shape you want to draw. In the 20s, a heart-shaped style was fashionable, with the cleft of your upper lip rounded just like...a heart. You can even ignore the corners of your mouth for a mouth that's more bee-sting--see silent film star Clara Bow (top left). She was famous for popularizing this style, and the lip-cleft was once even known as a Clara Bow though now it's more commonly called the Cupid's Bow.
In the 30s, lips were flattened. The slope of the upper lip was drawn gentler than when drawing a heart-shape, with the lines elongated and flared outside the bow. This is sometimes called a rosebud shape...see Joan Crawford (up left) or Bette Davis (up right) as examples of this shape. Moving on to the 40s, the lip shape stayed closer to the natural shape of the lip--in my observation, the edges of the bow were a little sharper. The difference from the 30s to the 40s wasn't quite as drastic as the change from the 20s to 30s. Take a look at Hedy Lamarr (below left) for inspiration. Tip: To achieve a sharp bow line, draw an X at the center of your bow.
I hope this is helpful--if nothing else it should help you skip right to the best part of Valentine's Day!
(One very helpful source for this post was the 20-to-40 Style Makeup Guide.)