In most Pagan traditions it is very important to purify or cleanse a space prior to beginning any sort of ritual. Although there are a different ways of doing this, how you do it will depend on the tradition you follow as well as what you feel comfortable with.
Usually, when ritually purifying an area, most do it deosil and spiraling inwards to the center. There are times when moving in a widdershins direction is appropriate, most notably for Banishing Ritual.
These methods are some examples of common ways to cleanse a space for ritual.
Smudging uses smoke, which will carry negative energy away from the area. Traditionally White Sage is used, however, other dried herbs can be added, such as Cilantro, Cedar, Lavender and Mugwort. The herbs are bound with string into a bundle, which is commonly referred to as a “stick”.
When lighting the bundle, try to make it flame for a moment if possible, then blow the flame out. This will leave you with a smoldering, smoking herb bundle. Once you have achieved the smoldering bundle stage it is time to smudge the house.
Now you don’t take the bundle and rub it on the walls and other things in the room, which would make a mess and probably ruin a few things and maybe even start a nice fire. What you do is this. Hold the smoldering bundle in one hand or in a heatproof object, like a shell. With either a fan or your free hand you waft the smoke to the edges of the room, making sure to get it into the corners.
When you have finished smudging you can either snuff out the smoldering end of the bundle by setting it into some sand or by crushing the end. An alternative method is to douse it under a bit of water, making sure to let it dry completely before attempting to use it again.
By long tradition, the broom is associated with cleaning and purification. The broom can be either a special one used solely for ritual cleansing or even your household broom. Use a broom or besom going around the edges of the space, with your intent being to sweep negativity away as you go. Here's a good idea. Start and finish near a door--that way, negative energy is swept outside, rather quite literally.
Asperging is the sprinkling with a liquid in order to effect spiritual and magical cleansing. Most people will associate Asperging with the Catholic Church, however the practice is also widely used by pagans for cleansing prior to rituals.
It can be accomplished in many ways. The simplest of these is to have a premixed liquid of your choice and bundle of fresh herbs that you can dip into the water. Then you take the herbs, dip them in the liquid and with a quick flick you throw the liquid off the herb and into area or onto the object to be cleansed. You don’t want or need to have a lot of liquid being thrown though. Just small droplets are perfect. Herbs that are prefect to use are Sage, Lavender, Vervain, Hyssop, Pine, Rue and Rosemary.
Another option that can be used quite effectively to cleanse a space is the use of incense. This can be either in cone form, stick, or powder and charcoal. The incense should be for working with cleaning, purification and even protection if you want to add that bit into the cleansing.
During your cleansing and purification of your space you can also include a little chant to augment the process. There are many to be found on the Internet as well as in books. You might even have one in mind already, in that case write it down so you will remember it for the next time you want to cleanse a room.
In addition to the above, I also ensure that the space is physically cleaned as well. I try to use a non-toxic homemade cleanser to do this. How you physically clean is of course up to you.