Long answer: Usually, I start off by thinking of a personality. My first questions are: "How would this character's personality reflect their design? Is this character prideful or relaxed? Evil or good? What element does their personality correspond with?" More questions come up, but an idea comes to mind. For this example, I'll refer to my self MOC, as it's the easiest example I can think of. Pictures can be found here. This character reflects my own personality traits while also reflecting some of my physical traits. I'm a small person, in size and weight, so I used that to make a smaller body shape for this MOC. I also decided on using the element of Sonics, as I am musically inclined, but I used the accent color of light blue instead of the usual reddish-orange because I like the color blue (and my eyes are blue). The claws on the back also help to reflect the element in the design, acting as tuning forks to draw in sound to be used as elemental energy. I went mostly with smooth texturing, as I prefer that design, which the use of CCBS helps to create (and I'm NOT using Inika torsos or sockets anymore; I've broken too many that I cannot use them without something falling apart in my hands). I gave him long legs because I, in real life, have longer legs in comparison to my body structure. In making MOCs, I usually make every bit a part of the personality. If the character is, say, strong and easily angered, I make the torso and limbs reflect that by providing some bulk. In my example, the character has a thin body structure, which indicates that he's fast but also has some strength behind him. One could say that the size and smoothness help him in being aerodynamic. Overall, I'd say to practice with layering and coming up a bunch of techniques that suit you. In other words, build your own style; try not to copy someone else and say you're done. Short answer: This is a question that is not easily answered in just a few sentences. It takes practice and it all depends on what you want to make.