Wiccan altars are a sacred space in which we put and use the elements of our practice. Sometimes is too obvious that we overlook the true function of the altar: connecting with our spirituality. Beyond technical issues, the objects and positions of an altar will depend on the needs and beliefs of each person. Nothing is essential, so everyone can use the objects they want and how they want, the ideal is to understand why things are that way, their symbolic meaning, and thus create your own altar according to your needs.
Having said that, I can tell that the objects of what should be included on Wiccan Altar are placed according to the cardinal points, the altar is usually looking to the east, where the sun rises. The north corresponds to the earth element, the south corresponds to fire, the east corresponds to the air, and the west to the water. Each cardinal point can be represented by an object significant of its element, for example, using transparent crystals (like crystal quartz) or a feather to represent air; a plant or sea salt to represent the earth, also stones like hematite and green aventurine; for the fire you can use a tiger's eye or a stone with colors like yellow, orange or red, also represented by a candle; and water, represented by blue or crystalline stones, a sea rock, or a cup of water.
Symbolically, the left side is considered the side of the feminine, of the moon, of the night, so on the left we put the representation of the Goddess, generally represented with a candle in the shape of a woman. While the right side is associated with the masculine, the sun, and the day, so it corresponds to the God with a candle in the shape of a man. Although you can also represent them by colors, white for the Goddess and black for the God. If you aren’t wiccan, you still can put the representation of you Deity in the center of the top of the altar. Moreover, it’s almost never missing an incense placed in a corner of the altar to purify residual energies before and during the ritual. In addition, there is also a candle snuffer on the altar, because blowing out the candles at the end of a ritual is considered disrespectful to the spirits of the air and the Deities.