I surround myself with circles of light that no negative energy can cross.
This illustration is the best I have ever seen to illustrate what we mean by surrounding ourselves with light. Some people imagine themselves in a bubble, a cocoon, or a dome, while others simply imagine circles of light that act like a kind of force-field through which negative energy cannot pass. Some imagine a ray of light from God that enters their body through the crown of the head. Other people imagine a circle of mirrors with the reflective side turned outward so that negative energies bounce back to the sender. When I surround myself with light, I also hear an inner sound that is a bit like the little twinkle sound that the computer makes in the Star Trek movies. Some people I know surround the airplane or car they are riding in for protection when they travel.
When we surround ourselves with light, we are not really building walls. Rather, we are actually raising our own vibrations, and when our vibrations no longer match that of negative emotions, people, or situations, we can rise above them, and they will no longer affect us.
Different colors of light have different desirable qualities. White light is actually all the colors combined. You probably did a science experiment in school using a prism that refracted the white light from the sun into the colors of the rainbow. White light seems to be an all-purpose color that is regarded as the highest form of spiritual protection available. (It's no accident that evil is associated with darkness, and that we speak of "heavenly light.")
Various colors of light can be used as therapy for a variety of reasons. All you have to do is find an image with the color you need and stare at it for a few minutes. The easiest way to do this is to go to Google images and type in a color, then just select and download the image or images you wish to use. If you know how to make your own screen saver or slide show, you can do this using several images of the same color.