Let's address what does not constitute proper psychic self-defense first:
Resisting what assails you is not proper self-defense on the psychic level. Resisting something makes it more powerful. This is the ignorant man's psychic self-defense; it comes with huge drawbacks and a psychic cannot afford it.
There are two aspects to psychic self-defense: internal and external.
The enemy that attacks us internally is popularly known as FUD - fear, uncertainty, doubt. Although outside sources can make FUD grow or subside, they can only do so if it already exists within. The proper psychic self-defense against our own selves is trough clarity, knowledge, and personal integrity.
Against external energy flows that attack us the essence of the proper psychic self-defense is to take a deep breath and let it go through. This way it does not grow stronger and the psychic gains valuable information. Suspending potential judgment and disgust is a must - a psychic cannot look away and hide.
Psychic self-defense is a matter of candor and courage.