Summarize the following:
Look over your sculpture and think about the different materials that would make up that object in real life (flesh, hair, fabric, stone, grass, fur, etc). On your original sketch or on an entirely new one, map out what textures go where. Do some research. Look at lots of pictures of those types of textures to figure out how they work. You'd be surprised how complex it can be. Fur, for example, grows in chunks and you'll have to pay attention to the length, organization, and direction of every chunk. Begin to texture your sculpture, one section at a time, using traditional or improvised tools. Only a very limited number of sculpting tools are needed and most can be improvised from common household objects. You will have to experiment to find out what works best for you, as almost every sculptor uses their tools differently.  Generally with sculpting tools, large tips are used to create the broad details, while finer tips are used to create details. Scoop-like tools create rounded areas. Tools with a loop are used to scrape away the material. Anything with a sharp edge can be used to cut. Tools can be improvised from: balls of tin foil, black peppercorn, toothpicks, x-acto knives, a toothbrush, a steel ball chain necklace, a comb, knitting needles, crochet hooks, large and small sewing needles, cookie cutters, melon ballers, etc. Once you're done with all of the major clay work, you'll need to cure your sculpture to make it hard (if you want it hard...if not, ignore). Different clays need to be cured in different ways (air dry, bake, etc), so follow the manufacturer's instructions for the clay you use. It is generally better to under-bake (use a low temperature for longer periods of time, if you can), to avoid burning.

Summary:
Identify the necessary textures. Texture the areas. Cure your sculpture.