Whether you practice Gardnerian Wicca or not, being naked or skyclad adds an element that provides so much more power during rituals when you have male and female hormones together at their peak for a period of time. This is great for raising a cone of power or creating a servitor, egregore, entity, ect.
Performing a ritual skyclad also allows the body to connect directly to nature. Clothing as well as shoes can inhibit the earths natural magnetic energies from interacting with your own energy field or aura. If you do have to wear your clothes at least make sure you are only wearing natural fibers as synthetic fibers will greatly effect a person in a negative way and if possible take your shoes off. This also goes for wearing clothing in your mundane life as well.