Anyone have any tips. I have a shirt that Im simming, and I'd like to be able to force some wrinkles in it. As far as I know, using a high compression stiffness is what is supposed to achieve that, but Im not making much progress by changing that parameter. Any tips would be appreciated.

There's a few methods. If there is enough topology, and the cloth has a low enough bend stiffness, it will naturally wrinkle. Then compression stiffness can help preserve those wrinkles.

Also, the vellum brush is a good way to add wrinkles as well. I used that on an animated alembic, to add wrinkles to that. Can potentially use that on a static alembic, then set the wrinkled geo as the new rest state. The cool thing about the vellum brush, is it supports collisions, so that we can avoid the interpenetration we would normally get when shaping the cloth on the body

Also, if your cloth has a low enough bend stiffness, it will naturally create wrinkles due to gravity. Then you need to balance it by adding stiffness. If you need additional wrinkles, they can also be added post sim, using the vellum brush. You might need to write out the sim first.

Scaling the rest length by a attribute should be able to introduce some wrinkling

In my experience, wrinkling is mostly a function of topology. It's got to be high enough to get accurate movement. Then bend stiffness determines how it wrinkles. High stiffness gets you leather or vinyl-like movement (less wrinkling). Low stiffness gets more detailed wrinkling.

Not surprisingly, garment construction also plays a big part in getting believable wrinkling, so pay attention to where your seams are.

Enabling warp/weft can sometimes be useful for keeping more stiffness along one axis (say along the vertical of a dress) and less along the other where you want more wrinkling.

A file would help if you have one.