This is a great one for doing in bed: if I get the start of a head cold coming on, I visualize energy coming in through the soles of my feet (as if there were little vents like a steam iron all around my feet) and then draw it up through my body and release it out the top of my head to the sky as if there were little vents on the top of my head. I usually take a breath in and imagine the energy reaching my waist, then on the breath out, have it release to the sky. I do that a few times and I'll notice my head starts to feel better. Then I can draw in energy from the sky to the top of my head and move it through to the soles of my feet out to the earth, again with the energy reaching my waist on the breath in, and moving out to the earth on the breath out. Then I alternate earth-to-sky and sky-to earth. This may feel hard at first, but the more you practice, the easier it gets. I used to get sick all the time; now I rarely get a cold.