Below is a simple Wiccan style ritual, that can be used for Esbats and Sabbats. Nearly every book and website will have their own version. Feel free to adapt the ritual to your own needs.

Step One : Proper preparation is essential, it's no good starting your ritual then realising that you've forgotten something. If you wish, you can print out a worksheet to help with your planning. Ritual Creation Worksheet

You need:
Altar Candle, Water Bowl, Salt Dish, Incense, Athame.
If you're not sure how to set up an altar then read Altar Setup

Light the altar candle and the incense, saying :
I light this Candle in the names of the God and Goddess and in the names of the four Mighty Ones,the rulers of the elements and in the names of the spirits here today, may power and blessing descend in this hour upon this place and those gathered here.

Touch the salt with tip of athame, saying:
Blessings be upon thee, O Creature of Salt; let all malignity and hindrance be cast forth from thee, and let all good enter within. Wherefore do I bless and consecrate thee, that thou mayest aid me. In the names of the God and the Goddess.
Using the tip of the athame, take three measures of salt and put it into the water, then stir deosil three times with the athame, saying:
I exorcise thee, O Creature of Water, that thou cast out from thee all the impurity and uncleanliness of the world of phantasm. In the names of the God and the Goddess.

Draw a circle, continuous from east deosil (clockwise) unto east with the athame saying:
I conjure thee, O Circle of Power, that thou be a boundary between the world of men and the realms of the Mighty Ones; a shield against all wickedness and evil; a rampart and protection that shall preserve and contain the power that we raise within thee. Wherefore do I bless thee, and consecrate thee, in the names of the God and the Goddess.

Walk round the circle deosil carrying the incense and saying :
Sylphs of the wind, I ask you to blow And bring on your wings the power to know.
Walk round the circle deosil carrying a candle and saying :
Salamanders of fire, I summon thee still To bring on thy flames the power to will.
Walk round the circle deosil carrying the water and saying :
Undines of water, come as I declare And bring on your waves the power to dare.
Walk round the circle deosil carrying the salt and saying :
Gnomes of the earth, I ask thee most humbly Bring from the mountains, your strength and fertility.

Stand facing East and say :
Guardians of the watchtowers of the east, spirits of the air, of the witches blade, bless us with your wit and wisdom, hail and welcome.
Turn and face South and say :
Guardians of the watchtowers of the south, spirits of fire, of the witches wand, bless us with your will and determination, hail and welcome.
Similarly, in the West:
Guardians of the watchtowers of the west, spirits of water, of cauldron and greal, bless us with your instinct and intuition, hail and welcome.
And in the North:
Guardians of the watchtowers of the north, spirits of earth, of pentacle, bless us with your protection and fertility, hail and welcome.

I stand before you to .... (state intent).
At this time you state the purpose of your ritual, to cast a spell, ask for healing, say a prayer, celebrate a festival or just say thank you.

When you feel that you are ready to finish you must close the circle.

Closing the Circle :
When the Circle's work is done, face East saying:
Ye Lords of the Watchtowers of the East, spirits of Air, I thank you for attending my rites; and I bid you to depart.
Repeat for the remaining Quarters, addressing each with the titles by which it was invoked.

Then say :
Spirits of the witches craft, I thank you for all of the aid that you have given me. In the past and in the now and in the days to come. Return to your abodes in the places between.

You must draw back the energy that you used to cast the circle, so walking continuous from east widdershins unto east with the athame saying: As I conjured thee, so I clear thee with the power of the witches blade.

Extinguish the altar candle.