When I first started my formal pagan education, it was with a Wiccan coven—a British Traditional group. One of the first things they taught me was how to ground, and this is the method my teachers used: while sitting in a straight-backed chair, posture erect but relaxed, feet flat on the ground, hands on thighs (the point was to have no body parts crossing each other), they had me put myself into a light trance. Next, they told me to visualize a cord firmly attached to the base of my spine. How you visualized it being attached wasn't really important, as long as it was firmly attached. Examples given were: a heavy link chain, welding, permanent glue – whatever you felt most comfortable with and could best visualize. Then send the other end deep into the heart of the earth. Attach it there with an anchor or anything else that you're confident will keep it there. As for the cord itself, it can be made of any strong material you wish, but should be a bright silver in color (it can even be a woven cord of flowers, as long as you're confident of its strength). Through this cord you can send surplus energy, negative energy (to be transformed by the earth), or have energy thrown at you without your will be automatically pushed/pulled down the cord.
While sitting upright, close your eyes and put one finger in the middle of your forehead and another, perfectly level with that point, on the back of your head, and draw an imaginary line between those points. Now put your fingers right at the top of your ears and draw a line between those two points. Where those lines intersect is the center of your head. Now be there. This is your space - your own private room. You are now centered: But are you done? Look around your private room. What does it look like? Are you standing or sitting? If sitting, what are you sitting on? Is anyone else in the room with you? If so, tell them firmly to leave. This is your space. If necessary, push them out. Now that you're alone, does your room need cleaning? If so, clean it and flush the debris down your grounding cord. Now you have a place where you can be at peace, do personal work, etc.
With practice you will be able to center yourself instantly without having to draw the lines, etc, but a periodic cleaning is always a good idea.
"HEALING" THE AURA
'Seeing' or sensing the condition of your aura starts in the same way, posture-wise, except the palms are up. (I was taught that besides the seven main chakras, there are four minor ones - one each on the soles of the feet and the palms of the hands.) Go into a light trance, open the crown chakra, spine chakra and all the small ones (I usually visualized each chakra as a dialating door, such as one occassionally sees in science fiction movies. Use what works best for you.) Through the crown chakra you send a tendril of thought to the center of the universe and draw power (visualized as electric blue). You do the same with the foot chakras, and draw energy from the earth (a blinding white). These two energies mix in your second (abdominal) chakra, and you send the mixed energy out through your hand and crown chakras into your aura, empowering it.
Now with your inner eye, scan your aura. Now that your aura has been charged, rips and weak areas should show up more easily. Sending more energy through the hand chakras, you now mentally 'press' the ripped areas together, visualizing the edges flowing together and becoming whole. For the weak areas, simply send more energy there, visualizing it becoming stronger, and reinforcing the area.
While doing all this, you may as well check to see if there are any cords other than your own attached to you. If so, try to sense who they belong to. Some 'foreign' cords you may not mind, such as those belonging to your children, lover/husband/wife, etc. However, that annoying person at work who makes you feel tired just being around them may have (entirely subconsciously) attached a cord to you through which they're drawing off energy (a psychic vampire). Take an energy sword and lop these off, then seal the 'wound' and block against a recurrence.
CLEARING OUT NEGATIVE ENERGY
Imagine a rose (Because that's the image I was taught to use. If you want to use something else, go ahead). See that rose as clearly as you can. This is a cleaning rose. This rose is going to sweep through your space (aura and body) and suck up the negative energy from that annoying person that just wouldn't shut up, or kept finding fault, or kept coming on to you, etc. It's going to absorb the energy caused by that reckless or rude driver that you encountered when you were driving. It's going to absorb the stored hurt from your childhood, etc. It's going to round up all sorts of negative energies. When it has absorbed as much as it can, throw it out in the middle of a field, or the street, and explode it, destroying all that negative energy at the save time. If you need another rose, go ahead and create it and let it get what was left over - then throw it away and explode it, as well. Keep repeating as often as necessary.
Just be aware that just as you didn't acquire all that negative energy in one day, nor are you going to rid yourself of all of it in one day. As you clean some away, more will surface. In time, however, you can succeed.
When you're done with that, imagine a big, golden ball (or sun) above your head. Have that ball start gathering up all of your energy that you've left around the various places you've been to, and with the various people you've interacted with. When you feel that your ball has absorbed all it can, bring it down to touch your head, and feel all that energy being reabsorbed into you; into your head through your seventh chakra, down your neck to your spine where it splits into four channels - two on each side of your spine - on down to your first chakra, and let a little bit go down your grounding cord as well, to clean it. Feel it spread out from your fifth chakra down first your right arm to your hand, then the left. Feel it going out first one leg, then the other. Then, when you're ready, stretch, reach down and touch the floor to ground yourself. Then go ahead and get up and move around.
A basic shield can be made by taking a 'ribbon' of cosmic energy (electric blue), and wrapping it around yourself clockwise. Have the energy about three inches away from your body, and make sure that all of your body is covered, including soles of feet, hands, and face. Of course we all know that we have to cover our butts, yes? *grin* Then take the earth energy (bright white) and start wrapping it about three inches away from the blue energy. This should be wrapped vertically, front to back. Again, make sure there are no gaps. This outer layer can be 'customized' to take care of any negative energy that impacts on it in any way you wish. You can give it its own grounding cord, mirror it to reflect the energy away, give it 'radar dishes' to reflect the energy into space or back to its origin, give it spikes to cripple the energy, etc. Visualize it being able to vary it's strength automatically, at need.
One should be grounded and shielded at all times. To begin with you may find that you need to keep re-establishing your grounding cord and shield several times a day, but over time your subconscious mind will take over the job of maintaining them, making being grounded and shielded automatic. Until then, check your cord and shield often, and your aura at least once a month.