This is a massive topic and I apologize for the length of this rambling. It isn't something that can be covered briefly however and I'm sure this discussion will still leave many questions.
Occasionally, either through a journey in the astral or contact with people in the physical realm, it is necessary to protect or cleanse yourself Psychically.
We've all known people who always seem to have a major crisis brewing in their lives right? What happens, is that some never have learned how to maintain their own energy or draw upon natural energies to keep themselves whole and in good condition spiritually as they should.
These people continually seek out others that will allow themselves to be attached to. They use a ploy of feel sorry for me, or come to me and I will give you access to the powers of the universe or any number of other pick-up lines that can be very convincing or tug at your heart strings. Essentially, these people, while we can and do have sympathy and concern for them are psychic vampires and we need to protect ourselves.
Have you ever spent time talking with someone and afterwards felt drained and tired. Guess what? You've just been tapped. In the magickal community, there are those who become very proficient at this skill and can attach themselves to you over great distances and maintain that attachment. The actual mechanics of it can be quite complicated to describe, so for now, just accept that it can and does happen. The same thing can happen on journey's into the astral too. If you are not focused and allow yourself to aimlessly wander in the lower levels negative entities inhabit, they can and will attach themselves to your energy centers and cause problems.
Either way, the result is that you increasingly begin to feel tired and all drug out. Your energy levels drop substantially and chaos can and will begin to occur in your life as well as the potential for growing health problems.
So how do we recognize and protect ourselves from this? Actually it's pretty easy. First off, you need to realize that your aura and your energy are yours. No one or nothing has a right to them unless YOU give them permission to attach themselves or you open your energy centers freely.
If they attempt to attach without your permission, it IS a form of Psychic Rape and needs to be resisted strongly and without hesitation. In the astral, you simply will them away or yourself into a higher level away from these low-level entities. It works much the same way as trying to put to equal ends of magnets together. It can't be done. If you truly want them to go away, they will.
Low-level entities in the astral will always try to attach themselves to you below the throat chakra, so this is a pretty good rule of thumb for what you may be dealing with. Higher level beings will ALWAYS offer a joining of aura and energy above the throat level. If one appears and asks or attempts to connect below the throat chakra, simply will it away or move to a higher level yourself, they cannot follow you there. The exception to this, is that you've encountered another human traveling in the astral looking for someone to tap into. Again, your energy is your energy and no one has the right to trespass if you don't want them to. Just say NO! and will them or yourself away. The astral is a magickal place and you can make anything happen there that you will to happen with skill and practice.
The key to avoiding low-level entities in the astral, is to trust your instinct and use common sense. If a contact makes you feel uncomfortable, move away and will yourself somewhere else. The purpose for astral travel is to contact guides or spiritual beings to learn and grow.
In the physical world, you can recognize psychic vampires although it is a little more difficult. People can be very clever at disguising it or they may not even realize that they are doing it. All they know is they feel bad and talking to you or spending time with you makes them feel better, so they crave being around you. You can still spend time with these people and care for their well being, just protect yourself. You can also choose to let them have a little of your energy to let them feel better, and then close off the flow. Ultimately however, it is best to not let anyone become dependent on YOUR energy so that they can feel good. It is much better to show them how to raise their own energy or draw it from mother earth and nature as we are supposed to do.
One of the simplest ways to prevent someone from tapping into your energy is to sit with your legs crossed at the ankles and then do the same with your arms or wrists or by holding your thumbs and index fingers of each hand together. This can be done very inconspicuously although you might get comments that you feel suddenly distant. What this does, is it closes your energy loop and keeps your aura and personal energy recirculating within yourself.
Contact between people should be an exchange of positive energy that makes both of you feel good about being around one another, it is a sharing of spirit and soul that benefits and energizes both of you, not just one. I bet quite a few of you are going Hmmmm, right about now... We've all experienced relationships like that and it can be difficult to bring them to closure especially if our hearts are involved.
In the case of an intentional psychic attack, it can be much more difficult to detect and deal with. It can happen through many avenues and if you feel or know that someone is trying to attach themselves to you. Break all contact immediately. These people, if allowed, will attach themselves to you astrally and completely drain you. They have no regard or concern about your health and well being whatsoever. They are Psychic Rapists and could care less about you and should be treated accordingly.
Now I'm going to depart a little from the usual Wicca "White Light" everything is coming up roses philosophy here. I am a Witch and have no qualms about zapping a psychic attacker when the need arises. Actually I just kind of reverse the energy their sending back to them which makes them kick their butt in a manner of speaking. Ultimately I'm just helping them zap themselves, so my karmic slate stays clean.
Ok, on to the meat and potatoes.
Strong visualization skills play a helpful role in this but they aren't absolutely necessary.
If you suspect someone is intentionally attacking you psychically, break all contact with them immediately and do not have any more to do with them.
For the beginner:
If possible, get out into nature and at a minimum, take off your shoes making as much physical contact with the earth as you can. Take deep breaths and relax. Feel the warmth and energy of the Goddess and earth flowing upward into your body, focusing your thoughts on letting it fill and refresh you completely. You are trying to enter a meditative state. Call upon the love and protection of the Goddess to fill and cleanse you. Feel it wash over and through every molecule of your being. Become one with nature and the earth. You can do it, smile.
The best that you can, visualize all negativity flowing upward and out of your body through the top of your head as the warmth and love from your connection with the earth replaces it. As this warm glow fills you, see and feel yourself being surrounded by a swirling white light of protection, positive energy and well being.
Will the negative influences away from you. You will feel yourself becoming more relaxed and cleansed as the negativity flows away. You will also intuitively know when to return to the physical realms of consciousness. When you do, give thanks to the Mother spending some time to enjoy the connection you feel and let the beauty of nature surround, fill and balance you.
For the intermediate or advanced:
Although I prefer doing this out in nature, it isn't necessary. Since I live out in the boonies, it's easy for me to go to one of my working areas and perform this cleansing and balancing skyclad. Your circumstances and environment will dictate.
If you are familiar with self cleansing or know someone who has developed these skills, either check your own aura or have them do it for you. Enter a deep meditative state and look for fluctuations, ripples or dark spots in your aura. You are also looking for thin auric threads attached to one of your chakras below the throat level indicating you have psychic lice.
Call upon the Goddess, your astral guides or animal totems to help cleanse your spirit replacing the negativity by feeling and seeing the same positive energy flow into you as described above. Fill and surround yourself with the swirling white light of protection, love and harmony as you visually sever the thread or threads breaking the connection. As the threads are severed, visualize a strong beam of white light pushing them away from you. If you are working with someone in this, they are softly talking to you, helping you visualize this as it happens. When done, spend some time in quiet reflective meditation and figure out how you allowed this to happen. You should have known better...
This topic is actually quite detailed and could lead off into numerous directions and good discussions. Time restricts this however, and I hope what's presented here is of value and help. Please exercise caution and common sense in your contacts in both the physical and astral realms my friends.