What you have to remember about evocation, or any form of magic for that matter, is that most of your external actions are a gimmick. When you reach the height of your power, you’ll be able to call on any entity with thought and energy alone. Starting out, your brain can’t reach that state automatically. So the rituals do a bunch of sub-conscious programming that overstimulate your mind. When you get into the trance state, the programming becomes the dominant thought. It’s also possible that the ritual steps are a form of sympathetic magic(as above so below).
What are you calling?
Most modern sources will have correspondence information for whatever you’re trying to summon. What direction to face, their element, colors, favored incense. How are they getting this information? Most likely channeling. But if you’re a beginner, this obviously won’t help you. So here’s another way.
Religious texts, folk lore, and grimoires contain the most important bits of information. What they look like conveys symbolism. What they do gives you a clue as to their element and possibly their personality. Offerings, candle colors, and incenses used are based on finding things that match the elements and astrological correspondence. If the entity is a god from a different culture, these factors are usually based on whatever was used by the original culture(the people who originally worshiped the god/goddess in question either channeled the information from the spirit or mapped it out logically like we are now).
By the time you’re calling on the spirits name you know who they are, how they act, and what their energy is like( even if it’s sub-conscious). The specific thing you need to contact is in a spiritual phonebook. Using a demonic language vs using latin or hebrew, or using culturally specific practices is like dialing the area code. As you get more and more specific down to the name and sigil, you have all the numbers. The theta gamma state hits the call button.
Which tools are necessary?
That’s completely up to you. Once you’ve work with a spirit for awhile their energy is archived into your memory. You can focus on what that particular type of energy felt like and pull it to you without all the psycho-drama you employed the first few times. Of course, you need to communicate with the entity and figure out how they prefer their summoning to be handled. We want to make our guests feel comfortable after all.
What are Currents?
Whatever you’re calling, your vibrations need to match theirs. If you call Satan, you’re tapping into energy that is demonic/infernal divine. Each tradition you work with have their own specific frequency. Theoretically, if you comment fully to a particular lifestyle or philosophy, you’ll resonate with that energy, then every being from that current will be easier to establish contact with and the bonds will be stronger.
That doesn’t mean demons will stop working with you if you change religions or that gods of one culture won’t work with foreigners. But if you really want to understand a spirit, it’s going to help you to immerse yourself. Understand the culture and mindset of the people that gained power from it. This helps humans bond and shows you respect them, so the same will apply to spirits.