I have been doing Polaroid 690 transfers for a few years. The best methods I have come up with involve completely dry paper. After testing a few papers, I now use Fabriano Acquarello Watercolour Artistico Extra White, in Gran Satinata Hot Pressed finish. This paper is ultra smooth and about the brightest art paper I have found.
I also found that to avoid a yellowing of the 690, I had to peel it upside down to avoid any light directly falling upon the film. If you still get some yellow areas after that, you can later take the transferred image to a sink, and gently rub the yellowish areas while running water across the surface. This can also work to lighten some areas of the transfer image, though it takes practice to do this carefully; otherwise you can remove parts of the image.
Probably the bigger issue for you at the beginning is rollering. I use a brayer that fits the narrower width of the Polaroid, and I have the sandwich of Polaroid and paper on a hard surface. First rollering is two minutes with steady and even pressure, then let sit for 30 seconds (giving arms a rest), and roller for another minute and a half. After that I let the sandwich of Polaroid and paper sit for a further minute or two, then gently peel starting at one corner. If you see some of the image coming up, you can roller some more, though not always effectively. Expect darker areas to want to lift off the paper, though sometimes there is no lifting at all and you get a completely clean transfer.
The reward of a well done Polaroid 690 transfer is very clean bright colours, and sharper than 669 details. The results have a unique appearance. After I figured out how to be consistent, I largely quit doing 669 transfers.
Polaroid 690 does not work well for emulsion lifts. Once you get the water hot enough, the darker areas of an image tend to melt away. There might be a way to be successful with 690 lifts, but I have yet to see any examples of that. Better to stick to transfers.
A G Studio