I suppose you could do this with any 2 decks, but a close friends and I happened to do this first using Tommie Kelly’s Forty Servants. This simple ritual will link 2 magicians through their decks.
First you select the card from your deck that you feel best represents your friend. For this example we’ll use The Witch.
Then they do the same for you, selecting the card they feel best represents you. For this example we’ll use The Thinker.
Now you physically swap these cards in your decks. So for the above example you would swap Witches, then swap Thinkers, so both decks are still complete.
This act of swapping the cards will put a little of your magick into their deck and vice versa, linking the decks, and the owners (obviously you don’t want to do this with just anyone).
Now just think (actively and passively) of these cards as the person they represent. The Witch in your deck is your buddy, The Thinker in theirs is you. Both of you should be reinforcing both beliefs however you wish, from meditation, to a simple thought whenever you draw the card, or even an offering to the servant.
Use that in any way you wish. You could use that card as a focal point in doing magick for that person, or reaching out and contacting them. It also gives the decks synergy for multi-deck readings.