There are a number of variations of this exercise, each more or less tailored to a particular belief system or to your elemental affinity. The simplest version is to bring up the image of a blazing white light and surround your body with it, up to arm’s length around you. You can “shower” yourself in it, or “cocoon” yourself, and it is best to practice with it on a daily basis so that you can bring it to mind whenever you feel anxious or threatened.
Some may find this exercise to be overly energizing. Blue light works equally well, and I have found that golden sparkles in the image, or a “champagne” color works better. Experiment until you find the color that works best for you.
There are potential side-effects from over-reliance on the white light or “barrier” methods of psychic protection. These techniques are good to practice, but they can function as barriers in other unintended ways. It is best to set the intention that only negative, hostile or predatory intentions will be blocked, while accepting healing, helpful, friendly and love-based energies to enter. You may find this balance takes some practice, but the effort will be a worthwhile one. Some people will always need this protection, and we all need it at times, but a strong sense of boundaries, good health, and good self-esteem are even more powerful tools to keep the bad stuff out and keep attracting the good stuff!