This is by no means intended to be a comprehensive study on Spirit Guides (henceforth called SGs for my sanity), but merely a jumping off point for your own studies…
Since the emergence of ‘New Age’ spirituality SGs have become heavily monetized and wide streamed. Because of this, many people may scoff or roll their eyes whenever the subject comes up, however they are still considered a part of shared human existence as virtually EVERY culture acknowledges them is some way or another. We often have several through our lives. Some may come and go, others stay with us from cradle to grave. It’s possible to have several at once, and they manifest most often in times of trauma, distress, and/or change. They can appear in literally any form, ranging from a gentle puff of a breeze leading us down a wooded path, to a fully fleshed visitation of deity (extremely rare btw). ALWAYS treat any SG with respect! The vast majority of them are harmless and only mean well, but there are some (mostly in the Deity and Ancestors categories) that can and will go out their way to make your life miserable if you cross them.
In general, a SG will fall into one of seven categories; Deities, half human/beast (think mermaids and centaurs), Animal Spirits, Angels/Fairies, Ancestors, Plants (I only hesitantly include and will explain later), and Ascended Masters. Some of these will overlap a bit, but you’ll see what I mean.
We’ll start with Deities because other than Ascended Masters, they are the easiest to invite in by choice. To invite a Deity to be your SG simply ask them. Typically this is done through formal ritual and offerings after much research. I cannot stress how important it is to know what you’re getting into here. You wouldn’t want to offer Ares flowers, or Krishna a steak. You wouldn’t want to petition Hera while cheating on your wife. Also, don’t expect thunder and lightning (even from Zeus), the Gods often touch us in odd, subtle ways, like a bountiful garden, or that extra spike of adrenaline during a race. They are also the most likely of all the SGs to get offended and take out their annoyance…The more you work with them the more you will see their hand in your life.
As SGs half humans can often overlap with both Deities and Fairies, but differ in that when they appear this way it’s normally as a more primal energy. For example; Calypso may appear as a mermaid, or siren, to help a rape victim through the trauma. Or Pan may manifest as a faun to a man trying to conceive a child. They seem to prefer dreams as a medium of communication, helping us defeat emotional obstacles, and overcome soul wounds. They tend to be the most transient of the lot.
Animal Spirits are the most easily recognized of the SGs as they are the most accessible in our daily lives. They almost always represent an aspect of ourselves that is coming to the forefront or rapidly developing. For example, a bear would be a logical SG for a new mother, fiercely protective of her cub. Or a cat, brave, curious, and independent for a young adult setting up their first home away from their parents. Maybe an owl, studious and wise, for a scholar doing a long-term research project. To figure out what your current Animal Spirits are (it’s not unusual to have two or three at a time), pay close attention to the animals around you. Are you noticing an abnormal amount of dogs? Did a woodpecker or hummingbird take up residence in your front yard? Maybe you discover a bee’s nest behind your garden. They can also appear in dreams. It’s not likely that you dream every day of having tea with a talking wolf or singing elephant…
Angels and Fairies are probably the most loved of all the SGs. Also called Light Beings they are also the only ones that you have absolutely no hand in choosing what so ever. Often they are with you from before birth and will stay by your side until you pass. They are the ones who will nudge you to go left instead of right, who give you tingles when you meet a person who you don’t want near. They are also the easiest to research. There are literally THOUSANDS of books and articles written about them. The problem becomes finding what works for you. Because this is the one category that is largely accepted by the Abrahamic faiths (at least the Angels anyway), many of said books are written from that view-point. While there is nothing inherently wrong with that, many pagans could feel uncomfortable with the ideologies of the authors. Generally speaking though, if your angel or fairy is willing to interact with you on a personal level, they tend to let you know. Meditation, yes/no questions with a pendulum, and tarot are all effective ways to communicate with this type of SG.
As a SG, Ancestors are exactly what they sound like. They are those who have gone before us, usually from our own bloodline. Many Paths include a reverence for our ancestors. It’s not an uncommon practice to leave a small offering when asking for assistance from this group. It could be flowers or pebbles at a grave, incense on your altar, or a food/wine offering. You know what your what your ancestors want best. This group also tends to be the most emotionally jarring. It could be your Grandmother’s face on that of a stranger asking for help (do it!), or your uncle appearing in a dream telling you not to buy whatever (listen). Their guidance tends to be very personal. Treat them with respect.
I include Plants cautiously. In my own path they are more of a tool to open myself to guides than a guide in and of themeselves. This catagory easily requires the most caution and research of any other. NEVER ingest or smoke a plant you know little or nothing about! I do not promote the breaking of laws (which simply the possession of some of these plants can violate). The most common (and legal) is fermented fruit juice (ie wine) and fermented grains (beer). There are many others that work to alter your brain chemistry and open your conciousness. The biggest danger is in long term recreational use. Many of these plants have a powerful effect, that if used too often can cause damage or become addictive. I highly recommend that if you so choose to use such things you do it with caution and respect.
Last, but by no means least are the Ascended Masters. This group includes Saints and/or those who have reached a greater spiritual enlightenment. Some examples would be Confucius , Jesus, Buddha, and (not joking) John Lennon. Some of these (mainly the Saints) you can petition to act on your behalf, but largely they guide us through the wisdom and teachings they left us.
I hope this has given at least the basic understanding of this extensive topic. Good luck and have fun in your research!