Doubleface card weaving is actually considerably simpler than it looks, by a good long measure. The basic principle is that you warp your deck up in two colours, with one colour in 2 adjacent holes and the other colour in the opposite holes.
Say it's white and black. You then set your pack with all of the white facing towards you and al the black facing away.
Now, to make a white-face cloth, you turn the whole pack forward for two turns. the white will now be facing away from you. To continue making plain white you then turn the whole deck backwards for two turns (for clarity, 90 degree turns)
Now, if you want to make some black come up on the surface, you take the cards you want to be weaving black and slide them forward, to make a second pack above the first.
Now, for clarity, when you're weaving white, what will happen is you'll first turn the white cards once so that all the white threads are on top. then turn them once more so the white threads end on the opposite side.
In order to create two colours, you turn the other pack in the opposite direction.
Say that you start with all white towards you, and you are weaving white with the front pack and black with the back pack. In this instance you will then turn the front pack forwards and the back pack backwards, for two turns. One both packs of cards have been turned twice, they will now be again colour-aligned in the same way as they were in the first place. You can now either continue, add more cards to the black pack, or take some cards back down to the white deck.
To make lettering and knotwork and so on is hereby reasonably simple, provided you work from graph paper. I have some graph paper printed from incompetech.org that is set up with the boxes longer than they are wide. each box represent a full 2-pick 180' turn of both packs. I simply move a ruler up to the next row after each 2 picks, and slide the cards up and down as necessary.
It's of course a time-consuming process, but the results are very satisfying. Also, I've found it's best when tucking the weft to leave a little bit out the side before card turning, then tucking it in before pressing the fell back. if you tuck after, then the weft is compressed and you have to pull it hard to take it in, which causes it to stretch out. Then the band just gets narrower and narrower and the selvedge threads end up getting way too tight. Only figured this out myself the other day. Of course, I was using lurex with an elastane ply in it, which doesn't help cause there's nothing elastane likes better than recovering from stretch ;-)
Also, you're better weaving this stuff on a fixed loom. I've also started using a comb behind the cards to keep each card's ends seperated. I'm actually using a bit of an industrial comb that must have been salvaged from a knotting setup at some point, but you can use a normal comb of some kind, and if it's pushing too wide, just turn it diagonal a wee bitty.
You can weave it back-strap but I've gone off that as it's next to impossible to create even patterns due to the difficulty in maintaining an even tension across the band. I'm sure you've got an inkle sitting about somewhere. If i'm weaving long bands I simply wrap the excess warp around the final peg several times and secure it with a half hitch. Do the same with the finished cloth. When you want to advance the warp, simply turn the wound warp forward the required amount and pick up the slack by doing the same with the cloth.
I have so far been using the whole pack in the S orientation, but I'm told you're better of orientating the cards S,Z,S,Z which apparently allows for smoother diagonal lines. Even so, I like the results I'm getting so far.