Contacting Spirits that move between the aetheric planes is a relatively simple process, I've found. Whether you're looking to speak with an archangel of a sephiroth, an earth-bound (i.e. goetic) demon, or a planetary intelligence, they're ready to talk and are just waiting to get in touch with you. The process is simple: draw the symbol that represents them, open a portal to their dimension, and then ask them to show up.
But why would you want to meet them? For years in my occult practices, I truly believed I had no interest in working with them. I would do a Lesser Banishing Ritual of the Pentagram (LBRP), and sure, that involved calling the four archangels that surround the throne of God, but then I would go on to do whatever ritual I had in mind at the time. Usually, this was either financially related or emotionally related. Either I was trying to get more money by landing a better job, or I was trying to bring peace to an emotionally chaotic situation in my life or in someone else's. Occassionally I would perform a healing ritual for my sick friends.
What I've found out lately is that I've always worked with "spirits." Whether they are gods of a pantheon, or a sigil I created in my harried Chaos Magick days, the fact is that I would summon intelligent autonomous entities to provide energies to create change according to my will. Since receiving this revelation, I've begun studying specific catalgues of spirits, and I've found an amazing set of well-defined, documented entities that have greatly expanded my ability to perform targeted magickal rituals.
Whether I work from the Goetia of the Key of Solomon, the Archangels of the Sephiroth, or the Olympik Spirits of the Arbatel, I've found that they are incredibly responsive and willing to perform their assigned duties as quickly as possible. This knowledge has translated to incredible power. Not the "power-mad, dominate the entire universe and reap untold wealth and glory at the expense of all others kind of power," the physics potential-energy power.
So why would you want to contact spirits in your magickal path? Because that's the way magick is done. All magick is based on contacting god in his infinite rays, or the representatives of his energies as they manifest in this world.
Are you trying to raise the tincture of your sphere to become a better person and advance in the Great Work? Evoke the spirits that exist in the realm of Atziluth of the qabalah. Their very presence will begin to transform your own sphere, raising your tincture (tincture refers to the vibrational level, the intrinsic quality) of your sphere, your soul.
Looking for ancient knowledge or hidden texts? The list of Goetic entities is replete with spirits capable of bringing you knowledge from the spheres. Entities from Briah and Yetzirah of the qabalah are also great at this. They bring books into your life related to the subjects you ask them about, or simply tell you what you need to know.
How about getting prosperous or getting health? The spirits of Assiah of the qabalah work at the mundane, physical level. Being closely related to the material realm, they are wonderful resources for manifesting wealth, health and prosperity.