There are two most common ways to set up an altar. One pertaining to the God and Goddess and one pertaining to the elements. The first is set up like so. The left side is pertaining to the goddess and has the feminine elements and properties such as earth and water. The right side represents the god and has the masculine tools associated with fire and air.
Left side (Goddess side)
Silver/White candle
Bell
Cup of water
Goddess statue
Crystals/Stones
Libations Dish
Right side (God side)
Gold/Yellow candle
Wand
Athame
Boline
Incense
Bowl of salt
Other items such as Oils and herbs may be placed wherever convenient. You may also want to keep your book of shadows close. The other way you may set up your altar is based on the elements. I prefer this method
North (Earth)
Green candle, Pentacle, Bowl of Salt, Stones, Plants, Flowers, Offering Cakes
West (Water)
Blue candle, Bowl of Water, Seashells, Chalice with Wine, Cauldron
East (Air)
Yellow candle, Incense, Feathers, Bell, Wand,
South ( Fire)
Red Candle, Athame, Boline, Anointing Oil, Candle Snuffer This is just two of the many ways you can set up your alter. The number one concern is to set it up to where it is accessable and the way you like it. Your alter is supposed to please you.