Lego Minifigs are made of 6 parts, the head, arms, hands, torso, hips and legs, allowing for several points of movement, the head, arms, hands and feet all move. The Arms and legs are further divided into right and left sides.
Since the inception of Lego Minifigs, there have been some further variations to this basic Lego minifig design. Most notably in the legs and hips, you can find variations with springs in the feet (from the basket ball series) and ones with magnets (from the movie series). Additionally women with skirts were commonly illustrated in mini fig for by using a 3x1x4 vertical column with an angled side. Additionally a pair of squat legs was designed for shorter Lego minifigs such as yoda, these however don’t allow for any leg movement at all.
Accessories, decals and head gear are also additional elements which make up the standard Lego minifig. Accessories can take the form of objects that fit into the mini figs hand, as well as items that sit on the head plug (such as back packs or capes), or fabric items such as gun holsters and robes. decals are the design element and one of the key ways to distinguish the sex of the Lego minifig, typically decals are found on the front and back of the torso, this along with the decals that go on the face form the basic ways in which a Lego minifigs personality and uniqueness come out. within Custom mini fig circles there have even been decals that go on the hands and arms that have been created.
In addition to these foundations Lego have also produced additional role specific Lego elements such as the ghost and skeleton as well as various other alien elements, and whilst these can be considered minifigs in the broadest sense their use within mini fig customization, at least for the moment seems limited.
Essentially by using these elements you can create totally customized minifigs that reflect a whole range of personalities. Below is a montage of some great examples of customized minifigs.