My advice is to have a frame and to work in layers. I use milliput as my sculpting medium, as it is both easy to use and (more importantly) cheap.
I would start out with making the body first, then sculpting limbs and appendages on later. My very first sculpting attempt was an ogre tyrant. I used wire and made a stick figure with some wire wrapped around the belly for additional support. It did not turn out well. It is very difficult to judge the proportions that are going to look good when you are just working in wire.
Start with a small bundle of cut wooden toothpicks. Chop them down to less than the total length of your expected body and glue maybe 4 or 5 together. Once the glue is dry, put a layer of milliput around your bundle, and try to get the rough shape of the body (but don't bother with details, yet). Once it cures, you can either apply another layer of milliput and sculpt all of the details, or you can start the limbs.
Hopefully this helps you a little bit.
