The New Age movement is very broad and therefore not easily defined. It is a humanistic movement (that initially spread through occult communities in the 1970s and 80s) rather than a philosophy with a specific set of beliefs. Still, there are some general issues that seem to be consistent throughout.
The "New Age" referred to is the Aquarian Age where man is supposed to evolve spiritually. In this, the focus is very much on man rather than on God. Man is considered divine, inherently good and in need of reaching his potential internally.
Man is also to be in harmony with nature. This plays out as more than just being careful and responsible. It can actually be a form of spiritism. Nature is considered to be spiritual as well. Overall, this movement is characterized by moral relativism and universal tolerance. Each person is to find his or her own reality and, through tolerance, produce peace and love. Regrettably, about the only thing that is not tolerated is the true God.
New Age philosophy incorporates elements of pagan worship including Eastern mysticism, astrology, palm reading, crystal healing, pyramidology, Western European paganism (Wicca), Native American spiritism, pantheism and nature worship. It sometimes includes linking up with aliens in an intergalactic consciousness. Some forms do acknowledge a cosmic Christ—that Jesus was a yogi and that he was trying to show us all how to be "Christs" like him. Some New Age practices also include psychic powers like levitation and efforts to contact the spirits of the dead. There is an emphasis on the acquisition of mystical knowledge.
There are many dangers here. For one, the New Age worldview is unbiblical and false, leading people away from the truth of God. For another, the occult practices mentioned above are really dabbling with evil spirits. Demons pose as the spirits of the dead, and they are also the ones supplying the power behind occult supernatural acts, often at first unbeknownst to the occult practitioner.
Moreover, the New Age movement runs directly counter to God's instruction. Notice what God told the Israelites when they entered the Promised Land. He had given them His laws and made it clear how they were to live. The people of the land they were entering had their own religious practices. God's warning to Israel was: "Take heed to yourself that you are not ensnared to follow them [the native people], after they are destroyed from before you, and that you do not inquire after their gods, saying, 'How did these nations serve their gods? I also will do likewise'" (Deuteronomy 12:30).
He then told them: "Whatever I command you, be careful to observe it; you shall not add to it nor take away from it" (verse 32). The same instruction applies to us today. We are not to engage in or adapt any of the religious practices of the peoples around us into our worship of God.