Casting a Circle

Common items used in spell casting are

• Candles
• Herbs
• Crystals
• Incense
• A particular day or time of the month or moon phase
• A spell 

Spells can differ between individual practitioners, but before any spell is cast,  you must create a circle of protection.

The practitioner would start by cleansing both themselves and the space they work in. They would bathe beforehand and meditate. Oils and incense can be used to cleanse the work space.  

A circle is cast to protect the witch. 

First, you want to decide where to create your circle.  Whether you have an altar or just a peaceful corner of your home – or maybe outside in nature – pick a place where you are undisturbed so that you can focus and work in peace.
It’s not necessary to mark out your circle, but some like to do it for ritual purposes, or for protection.  You can create a circle of rocks or crystals, or sprinkle sea salt along the edges of your circle, or place candles around you – for example five to mark out the points of the pentacle, or four placed at the cardinal points, West, North, East and South – also representing each of the Four Elements.  It’s up to you how you like to mark out or decorate your circle.
Stand in the middle of your circle.  Relax and breathe deeply.  Imagine that your crown (the top of your head) opens up like a funnel to receive divine, white light.  Your crown is always connected to the divine and to your Higher Self, and you can open up and amplify this channel at your will.
Open your arms, palms facing out.  With each in-breath, visualise yourself pulling down pure, divine light through your crown, and as you breathe out you channel this light out through your palms to create a protective shield around you.  As you fill the space around you with this high-vibration energy you may feel a tingle or buzz, you may get goose bumps, or you’ll feel light and uplifted.
Now hold one arm outstretched (the one you write with) and point to the edge of the circle.  Spin around clockwise three times, mentally marking out your circle with the divine light.  Then raise your arms above your head and say:
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“I ask that the God and Goddess bless this circle
So that I may be free and protected within this space
So mote it be”

You are now ready to cast your spell or perform your ritual.

source:http://wiccanspells.info/learn-wicca-basics/casting-a-circle-protection/