This is a practice designed both as a meditative practice and as a means of further developing the faculty of concentration.
Place a lit candle at approximately eye level and darken the room appropriately. Find a comfortable position and focus complete concentration on the candle flame.
If you keep your eyes open, you mind observe a sensation of merging with the flame. If you close your eyes, focus upon the after-image in your mind and try to maintain that image as a visualization exercise.
After some practice with these basic exercises, you may wish to extend the visualization with eyes closed of the flame of light growing and encompassing your body. This can be imagined as purifying and as protective.