Psychic Spirit guides can be a very diverse group of entities. Some human, some non-human. Non-human guides can evolve with humanity, but are not part of its life stream. Angels, devas, nature spirits and totem animals, are examples of this. They can have a very real and subtle influence upon you.
The human kind of guide can be living or dead. The living we may encounter as ordinary individuals who are out of their bodies, at night while we are asleep. There can be individuals who have trained themselves to consciously leave their bodies and withdraw their energy and consciousness to those more subtle realms through astral projection. Life masters, adepts or individuals who are spiritually developing, and very aware in a psychic sense.
This type of spirit guide are individuals who are still living within the physical. Encounters with this kind of guide are often not as recognizable as those who have passed over such as family, or friends. This type of psychic spirit guide can also be those who are preparing and waiting to reincarnate. Contact with this type of spirit is through the etheric and astral energy left behind by the deceased as they withdraw from physical life, ghosts and apparitions can fall into this category.