Our human aura is like an egg if someone can perceive energy directly, the shaman Don Juan Matus mentioned in Carlos Castaneda's book A separate Reality, can perceive energy directly and he says it looks like an illuminated egg.
There are 7 layers in our aura. When we use meditation and try to 'clean' it, we have to clean every layer. Many new age mystics just tell you imagine and visualize a white light coming down and engulfing your whole aura, this sometimes doesn't work well.
I usually clean every layer as I go along. Start by doing some kind of relaxation procedure like counting 1 to 10 or say to yourself, upstairs, downstairs, over and over again until you feel bored and sleepy,or you can get some to help you get to alpha or theta brain states.
Once you done that, mentally say to yourself "I am at level 1" and move your awareness from head to toe or vice versa, the idea is to scan your level 1 for blockages, once you sense 'something there', move your awareness to it, it should 'melt' or disperse.
If it is still there, try breathing it colors, you have to experiment with the color that will remove the block, repeat the same procedure with all other level, for example; I am level 2, I am in Level 3, etc.
When you say this, you are telling your mind to adjust to the next level using intent, Intent is the force that changes the level. Some times if you are at level 1, and you sense something 1 feel in front of you and you cannot get it off, and you try the usual color breathing method, this could be due to the fact that this blockage is actually at some other level - for example - Level 3 and you can usually remove the block if you move your awareness to level 3.
Sometimes when you move your awareness into the blockages, you get 'impression' like a past event or sometimes it plays like a movie in your mind's eye, this is usually the reason for the block.