The last of the four primary factors, this one quite literally separates the men from the... ladies. The word "feminine" is used to describe the 'softer' qualities and characteristics of a lady (and to some extent a man) that distinguish her as a lady, as opposed to anything about her that removes or conceals this fact (such as very short hair, trousers/pants, baggy tops etc.). I realise that some may consider these remarks sexist or old-fashioned, but the classical and conventional idea of a lady is someone who wears dresses or skirts, has much longer hair than a (conventional) man, wears footwear with a heel to accentuate the calf muscles and buttocks, and more often than not emphasises her facial features with cosmetics.
The extent to which a lady feminises herself is often in direct relation to the kind of clothing, hairstyle and makeup she chooses. In terms of clothing for example, a long flowing dress with a flowery pattern would be considered more feminine than a calf-length panel skirt, which in turn would be considered more feminine than slacks. Fabrics also play an important role in creating the idea of femininity. For example, lace, light cotton, organza, angora wool, silk and satin are all "feminine" fabrics, whereas linen, heavy cotton and denim, leather (sexy, sometimes, but feminine, no) and polyester are not feminine. Possibly the best examples of feminine clothing can be found in wedding dresses. Designers and manufacturers of wedding dresses and gowns go to great lengths to ensure their dresses make the bride look as feminine as possible. This isn't just true of the western world, but can be seen in virtually all cultures where the bride dresses up.
Just as clothing can make a lady look more feminine, so too can her hairstyle. Long flowing locks are generally considered more feminine than a short bob, bun or pigtails. Simple touches like adding flowers or a ribbon can add even more femininity. I'm not at all sure if style makes a difference, but essentially, the longer the hair (within reason), the more femimine it looks.
Colours of fabrics can also play a role in this area. Pale, pastel colours are considered more feminine than bright, bold colours and monotones. The choice of colours with makeup can also add to the feminine ideal, with soft natural colours for eyeshadow, lips and blush, and cleverly applied eyeliner and mascara.
Perfume can also be very feminine if it's light, fresh and perhaps flowery, although perfumes that are very heavy and overly sweet can fail to achieve the feminine effect.
There is also a side to femininity that does not require clothing or bodily adornments, and that is how a lady acts. Not so long ago, a lady from a good family was required to learn music, art, needlework and perhaps a few other feminine or 'gentle' pastimes. In other words she was expected to act "like a lady". These days a lady is generally only as restricted in her work and leisure pursuits as she wants to be, but can choose to accentuate her gender if she wants, either by how she dresses, how she acts, or both.