The first thing you have to learn is that you must believe and have self confidence. If you don't believe that magic gives you the power to reshape the universe, you're wasting your time. If you believe a spell or ritual won't work, it won't. And if you do believe in the power of magic, then you need to realize that when you use it you are putting your hands on the same forces that move the tides and spawn tornadoes. And that by doing so, you have the potential to harm yourself or others.
Here are a few basic techniques for protecting yourself and your home. They are also useful anytime. For example, there's no better night's sleep than in a room that's been magically shielded to keep out psychic noise.
The word cloaking is very useful in learning the technique. If you want to cloak your aura, yourself entirely, or a specific part about yourself, simply visualize a cloak or something similar molded around what your trying to hide...sometimes you can do this by enchanting an object that you are wearing. If you are trying to hide yourself, then it's helpful not to make eyecontact with the things you are trying to hide from. Blend into the darkness, and walk softly. It's possible to cloak cars, which can be helpful when traveling, but do not cloak it so much that other cars do not see you and run into you. While enchanting it, only cloak it from 'enemies', or so on.
This is a technique for creating a magical 'force field' around your person or a place, to keep out unwanted energy. This could be psychic 'background noise', nasty astral critters, or magical energy directed at you. Many people do this unconsciously all their lives. Others of us have to learn how. The method I use is to visualize a black 'force field' of energy around the area to be shielded. Some find it helpful to actually visualize an actual sheild. Remember to 'see' it in 3D, a sphere rather than a circle. (This is where those visualization exercises come into practical use.) I generally use my personal energy to power it, but it is possible to use any element. Earth is extremely useful in this. I visualize negative energy being absorbed by my shields, bouncing off, and flowing into the earth. ("Ground and Center" here.) I visualize it as porous, though, so that energy I send can pass through. With practice, you will be able to shield yourself instantly, without thinking.
When shielding your skin, you can visualize your skin forming into scales, or even armour. The more energy and focus you put in these things, the more powerful they are.
I have found that exhaustion, alcohol, sickness, or depression quickly erode my ability to shield, so keep this in mind. Once you have shields, there is lots of nifty magic you can do with them. You can turn cause the shields to reverse magic/energy back at people. You can set up traps. You can cause your attacker to become confused when he attacks, the list goes on and on.
This is a similar technique. I define a Ward as a Shield anchored to a physical place. Instead of using your energy, though, you let Earth energy flow upward to power it, though most elements can be used if you know how. With practice, you can create a stable, Earth-powered shield. This leaves more energy for spell work, or allows you to drop your own shields and recharge. Reinforce the visualization regularly, and it can be permanent, to protect your Circle, home, or camp. Some tend to anchor wards with physical objects-a stone, carved runes, etc. But it is the visualization that really matters. If the mental image fails, the shield will fail, no matter how many runes you carve.
Occasionally, when going about my daily life, I will feel a 'tickle' at my aura as some kind of psychic energy contacts it. Other times, the hair stands up on the back of my neck, and I quickly raise my shields. And on rarer occasions, I feel a sudden energy drain as my shields go from standby to maximum power before I know what's happened. In these situations there are a few shielding tricks I use. First is the mirror. I visualize the outside of my shields as a perfect mirror, reflecting any energy back to it's source. Next is making the inside of my shields a mirror. I use this to contain any psychic energy I might be emitting, hopefully making myself psychically 'stealthy'. Last is the 'iron wall' or 'stone tower' visualization, changing the thin energy shield into a massive fortress. This requires a lot of power, but when huge waves of negativity are breaking over you, it really helps.
Unfortunetly, there is only so much can be done on the defensive end, especially with us.
Now on to a few active techniques. If negative energy keeps coming at me, I don't sit back and continue to shield until exhausted. Any purely defensive battle is doomed, if it goes on long enough. This is the time where you should turn the defense into offense, which will be another post all together.
But, you can also invoke your deities, your animal spirits, your protection/guides, ect and so forth...when I say invoke, I mean 'invoke the power of', but you can also channel them if you feel it will help.
Malevolent entities (whether astral or earthly) tend to avoid the presence of the Deity. In fact, the nastier they are, the faster they sometimes run. But like most kids, I don't like bothering Mom and Dad all the time with small problems I've been taught to handle myself. We all need to learn to fight our own fights without calling help.
A basic technique is calling 'White Fire.' This is the Light energy of the universe, the silver-white of the Moon and the fire-white of the Sun, the sum total of the magical Elements. Let it flow in from all around you until you feel like a ball of lightning, then send a directed bolt of it back in the direction the negative energy came from. While the mind alone is all you need to do this, I find a sword/athame or a staff or wand are perfect tools to direct your energy through. If this doesn't work, you can still call on the Gods and Goddesses in their warrior/protector aspects to help you.