The following is a large chunck of "Chapter 7- The Magic Circle and the Alter" from Scott Cunningham's Wicca: A guide for the Solitary Practitioner, pages 57-61.
The circle is usually nine feet in diameter, (nine is a number of the Goddess) though any comfortable size is fine. The cardinal points are often marked with lit candles, or the ritual tools assigned to each point.
The pentacle, a bowl of salt or earth may be places to the North. This is the realm of Earth, the stabilizing, fertile and nourishing element which is the foundation of the other three.
The censer with smoldering incense is assigned to the East, the home of the intellectual element, Air. Fresh flowers or stick incense can also be used. Air is the element of the mind, of communication, movement, divination and ascetic spirituality.
To the South, a candle often represents Fire, the element of transformation, of passion and change, success, health and strength. An oil lamp or piece of lava rock may be used as well.
A cup or bowl of water can be placed in the West of the circle to represent Water, the last of the four elements. Water is the realm of the emotions, of the psychic mind, love, healing, beauty and emotional spirituality.
Then again, these four objects may be placed on the altar, their positions corresponding to the directions and their elemental attributes.
Once the circle has been formed around the working space, rituals begin. During magical workings the air within the circle can grow uncomfortably hot and close-it will truly feel different from the outside world, charged with energy and alive with power.
The circle is a product of energy, a palpable construction which can be sensed and felt with experience. It isn't just a ring of flowers or cord but a solid, viable barrier.
In Wiccan thought the circle represents the Goddess, the spiritual aspects of nature, fertility, infinity, eternity. It also symbolizes the Earth itself.
The altar, bearing the tools, stands in the center of the circle. It can be made of any substance, though wood is preferred. Oak is especially recommended for its power and strength, as is willow which is sacred to the Goddess.
The Wicca don't believe that the Goddess and God inhabit the altar itself. It is a place of power and magic, but it isn't sacrosanct. Though the altar is usually set up and dismantled for each magical ritual, some Wiccans have permanent home altars as well. Your shrine can grow into such an altar.
The altar is sometimes round, to represent the Goddess and spirituality, though it may also be square, symbolic of the elements. It may be nothing more than an area of ground, a cardboard box covered with cloth, two cinder blocks with a board lying on top, a coffee table, an old sawed-off tree stump in the wild, or a large, flat rock. During outdoor rituals a fire may substitute for the altar. Stick incense may be used to outline the circle. The tools used are the powers of the mind.
The Wiccan tools are usually arranged upon the altar in a pleasing pattern. Generally, the altar is set in the center of the circle facing North. North is a direction of power. It is associated with the Earth, and because this is our home we may feel more comfortable with this alignment. Then too, some Wiccans place their altars facing East, where the Sun and Moon rise.
The left half of the altar is usually dedicated to the Goddess. Tools sacred to Her are placed there: the cup, the pentacle, bell, crystal and cauldron. An image of the Goddess may also stand there, and a broom might be laid against the left side of the altar. (Some Wiccans-Particularly those reclaiming women’s spirituality- may also place labrys {double-headed axe} there as well. The labrys is symbolic of the phases of the Moon and of the Goddess. It was extensively used in Crete.)
If you can't find an appropriate Goddess image (or, simply, if you don't desire one), a green, silver or white candle can be substituted. The cauldron is also sometimes placed on the floor to the left side of the altar if it is too large to fit on top.
To the right side, the emphasis is on the God. A red, yellow or gold candle, or an appropriate figure, is usually placed there, as are the censer, wand, athame (magic knife) and white-handled knife.
Flowers may be set in the middle, perhaps in a vase or small cauldron. Then too, the censer is often centrally situated so that its smoke is offered up to both the Goddess and the God, and the pentacle might be placed before the censer.
Some Wiccans follow a more primitive, nature-oriented altar plan. To represent the Goddess, a round stone (pierced with a hole if available), a corn dolly, or a seashell work well. Pine cones, tapered stones and acorns can be used to represent the God. Use your imagination in setting up the altar.
If you're working magic in the Circle, all necessary items should be within it before you begin, either on the altar or beneath it. Never forget to have matches handy, and a small bowl to hold the used ones (it's impolite to throw them into the censer or cauldron).
Though we may set up images of the Goddess and God, we're not idol worshippers. We don't believe that a given statue or pile of rocks actually is the deity represented. And although we reverence nature, we don't worship trees or birds or stones. We simply delight in seeing them as manifestations of the universal creative forces-the Goddess and God.
The altar and the magic circle in which it stands is a personal construction and it should be pleasing to you. My first Wiccan teacher laid out elaborate altars attuned with the occasion-if we couldn't practice outdoors. For one Full Moon rite she draped the altar with white satin, placed white candles in crystal holders, added a silver chalice, white roses and snowy-leafed dusty miller. An incense composed of white roses, sandalwood and gardenias drifted through the air. The glowing altar suffused the room with lunar energies. Our ritual that night was one to remember.
May yours be the same.
also from the book
Amy Cat's Personal Alter :)