In a dualistic existence, we are only as susceptible to negative energy attachments as we let ourselves become.  Most people are unaware of this aspect of their existence and so may host many energies and spirits that do not serve their highest good.  Such is the nature of life on Earth at this time.  However, that being said, it is not at all difficult to rid oneself of these energies.  An invocation is usually enough to banish most unwanted spirits/energies from ones field and may be repeated as often as is desired.  The article below goes into detail on the mechanics and techniques of this practice.
One need not become excessive in their use of the invocation — typically once a day is sufficient.  Also, it should be noted that as one reaches higher levels of vibration/frequency, they become more resilient towards these lower energies and hence will naturally repel them to some extent.  However, even those highly conscious and evolved souls can benefit from regular clearing of their field.  Furthermore, if one has never before performed such an invocation, no matter what level they are at spiritually/vibrationally, they will likely find it to be of great benefit.  I can still remember the first time I performed one — it literally felt as if a 100 pound weight was lifted off my chest.  My life changed dramatically from that point forward — my health improved, my clarity strengthened and my mood became infinitely more stable.
An important thing to note here is that we can have negative energies from other people — including friends, relatives, parents, loved ones, etc. attached to us in addition to any spirits or implants and it is important to include these energies in any invocation/clearing, as they can affect us to a very substantial degree as well…

Psychic Protection: Immunise Yourself Against Negative Energy
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Have you ever entered an empty room, or office, and felt “uncomfortable”? Feeling perhaps quite happy to get out of that room, or office, as soon as possible? Maybe you have found somewhere that feels “bad” at one time yet feels “okay” at another time? This could be where we work, live, or somewhere we are visiting or passing through.
What about people? Do you know anyone who seems to have a “negative” aura? When­ever you are near them you feel more depressed, angry or fearful, than you normally do? How about the opposite? Do you know anyone who seems to make you feel better just by being around you, not even needing to say anything to you to improve things?

Apart from feeling worse around certain people and/or in certain places, do you find that you sometimes lose a lot of energy (psychic draining) in these circumstances? Do you have a problem with such things as insomnia, poor sleep, nightmares or low energy levels? Perhaps you are constantly lacking in energy? Maybe being diagnosed as having chronic fatigue? Or maybe you always seem to be getting colds, illnesses or other problems?
If the answer is “yes” then chances are you may be under intentional, or unintentional, negative psychic influence. What some people call being under psychic attack. Can anything be done about such situations? Yes, psychic protection is what one can learn to counter such things. Before talking about psychic protection however, we may wonder what it is and how it works.

To better understand this we need to understand these negative influences. Put simply they are usually categorised into two types. Thought energies (or if they have a shape – thoughtforms) and negative spirit influence. Now, you may instantly think I am talking about dead people. I am not. We are all “spirits”. Some of us are physically alive and some of us aren’t. We do notbecome a spirit when we physically die. We are already one.
One may also say, “But I cannot see/hear spirits. This is proof they don’t exist”. Well, I cannot see radio, or television waves in this room. Does that mean they aren’t here? I wouldn’t think so. Much the same as hearing. I cannot hear a dog whistle. But dogs can! It would be rather foolish for me to conclude such a whistle made no noise simply on the grounds that “I didn’t hear it.”

Negative thought energies are created by someone (dead or alive) thinking negative thoughts, e.g. anger, hatred, fear etc. If the person is thinking these thoughts about us then they are automatically projected in our direction. In addition, as negative spirits are attracted to negative energy these people will often accompany the energies. Particularly if this is done “formally”, i.e., a spell.

Fortunately there is defence against these things. Positive energies will dissolve negative ones and we can arrange for positive spirits to help protect us against negative ones. There is nothing particularly profound about it. To cancel out a fire, water is a good response. The principle of using the opposite response to a spell is along the same lines.

The negative thought content of a spell, or any other form of psychic attack, can be “cancelled out” by directing a positive thoughtform of the same, or greater, strength at it. When they meet, the negative thoughtform will dissolve. This can be achieved by such things as prayer, visualisation, etc. A common example of the latter is to imagine you are surrounded by a “protective” bubble of light. One can also imagine oneself being a hot ball of light. Like the sun. Radiating a hot, bright, light outwards.
The effect of negative entities can be “can­celled out” by positive entities of the same, or greater, strength. If the positive spirits predominate then many of the negative entities can be “cleared” (permanently) to spirit worlds.
Getting help from positive spirits is arranged by requesting it. Prayer in other words. It should be remembered we can do more than arrange “protection” this way. A good wording for such a prayer, and a list of recommended approaches is at http://home.vicnet.net.au/~johnf/aprayer.htm 

For those without internet access here is a way of arranging this, say/think:
“I ask the Divine Light Forces (Forces of God) for…
(1) Protection against all that is not of the light (alive and dead).
(2) Healing on all levels
(3) Guidance with my life. Especially in the area of ____________________ e.g. knowing what I should be doing spiritually, help with becoming a channel for love, light, healing, guidance and inspiration. Preparing for meetings and/or seminars etc.
(4) Divine love, light and healing en­ergies to go to __________________ (people we live/work with) as well as all who are working against our spiritual progression.

Other points worth noting :
(1) There are some interesting books on this topic in­cluding a booklet I have written. The authors range from psychics to medical doctors, psychologists, psychiatrists, etc. 
(2) Light coloured clothes tend to en­courage light coloured energies. For best health never wear dark colours.
(3) If someone is currently sending you negative effects, as in a spell, then you need to direct light, etc. to them constantly until you feel they have stopped. If you “clear” yourself today then there is no reason why they cannot dump you with new discordant energies tomorrow!
(4) Negative thinking/emotions such as anger, fear, etc. weakens our aura and reduces our “protection”. Positive thinking/emotions such as love, etc. strengthen our aura and improves our “protection”.
(5) Keep in mind that things take time. Some people think praying for one night and imagining white light around them for five minutes will solve all their problems. This is unlikely. Suppose discordant effect had built up around you and/or your house for ten years. Do you think it reasonable to expect it to go in five minutes? Think of it this way. If you had a blow torch could you melt an ice­berg? The answer is, of course, yes, but it would take more than five minutes!