The base layer is basically the clothing that sits directly on your skin. Make sure that you are fully protected from the cold but at the same time your clothing should be able to breathe so that sweat or moisture does not get trapped inside. Cotton should not be used for any of your layers while skiing. Use a nice pair of non-cotton long underwear on top and bottom.
After putting on the long underwear, put on some synthetic or woolen socks. Make sure to allow the bottom of the long underwear to sit over the socks. Now put on the fleece layer and ski pants. You can use a nice fleece sweater or pull-over to keep you warm. If you want, you can tuck the fleece liner in to the ski pants to avoid snow from getting inside.
Put on your soft or hard shell jacket over the fleece layer and ski pants. Make that you can easily move around with the jacket on. Now put on your wool glove liners, scarf and hat. Once you are done, put on your ski gloves and boots. Do not tuck the long underwear bottoms in to the boots as this can cause problems to your blood circulation.
You can easily alternate between layers while you are out skiing. If you begin to feel hot and sweaty then you can remove a single layer to cool down a little. However, make sure that you do not take off too many layers while out in the snow.