The attunement method I use is one that I think is most common because it's so easy.
First, you create sacred space. You can cast a Wiccan/Witch's circle like Tom suggested, or you can just create a large sphere of white light and the Violet Flame. You can just see it as a bubble, or you can shine a light out from your heart chakra out, creating a sphere of light around you
After that, you just use your imagination to create the person you're attuning in front of you. If you're not sure what they look like, just make a person of light with their name, location, etc. in it.
Run Reiki through all the chakras, the channel, and the aura and remove any blockages. Be sure to fully open/activate each chakra! I do this by addressing a chakra, and telling it to open and activate to the fullest extent possible. Don't forget the hand chakras. Open up the aura as well by filling it with Reiki. The Channel runs through the center of all the chakras as a white cord, it goes down to the center of the earth, and then up to the different dimensions. Clear it of any seals and blocks.
I put the symbols in the chakras starting like this. Heart, third eye, crown, throat, solar plexus, sacral, and then root. From there, I put the symbols in the hand chakras, and then in the heart again.
Here's why. I open the heart so that the person is open to receiving Reiki fully. Then the third eye to open them up to consciously experiencing Reiki, then the crown to open their channel for it, and then I get the three lower chakras in descending order to ground it in. You can put the symbols in the aura as well to make it easier to channel Reiki with their aura.
Another method is to do the same thing, but use a physical proxy like a teddy bear or a doll to represent the person
Before you attune someone, you may want to do like I did and ask the Universe to provide you with a holographic practice human of light to try it on. It's not a real human, but it's built just like one for you to practice on. If you speak to it, the reply will be direct from the Universal Consciousness.
If you go to the Manuels page, there are some good ideas that you can turn into distance attunements by replacing the real person with an imaginary one
Hope this helps!
Highest Blessings,
-Wes