I do pre-wash everything but the pre-cuts. I have a serger so I put a narrow serge along the cut edges. I have also run a narrow zigzag along the cut edges before I had the serger. I tried a straight stitch and it was OK, but the close & narrow zigzag seemed to do the best. I keep the stitch inside the 1/4" so I don't have to worry about pulling out all of the threads before I want to use it.

I don't know about the corner clipping. I have not tried that method. I would guess the pinking shears would work. My hands don't like to power the scissors. I do have a rotary cutting pinking blade, but I'm to lazy to change it every time I want to pre-wash fabric. (I know, but I'll run a line of stitching! Yeah, yeah, yeah.) I have found that most of the raveling happens in the washer. If I do wash fabrics that haven't been sewn, and I clean them up before I put them in the dryer, they don't seem to get any worse.

Best of luck on finding what works the best for you!