On an "energy" level, protection and cleansing can be achieved through visualization and intent. About 20 years ago, a book crossed my path which had a visualization for a "circle of protection", and so, even though my visualization abilities were not strong, I followed it and tried my hardest to try to picture a "bubble" encompassing me. Over time, I was able to see this "bubble" or "shield". After more time passed, at least 5 years, and all that time feeling drained for keeping this around me and feeling the need to "recharge" it periodically, I realized that this was not necessary. As long as you have it there and are aware that it is there, that is all that is necessary.
As for the cleansing, I incorporated this into my "shield" to only allow white light in and negativity, or darkness, out. This was my preferred method.
As for method and technique, the best thing you can do is try your own spin on what feels right for you. No matter what you try (speaking strictly on an energy level, not physical level) will work provided you supply the intent.
Just KNOW what you are doing is working, and it will work. Meditation, in any form, will greatly improve anything you do to cleanse and protect yourself or others.
I know this can be expanded upon, so if you have further questions, I (or anyone else, I'm sure) will be more than happy to chime in and answer.
Lady of Light