I have an old machine & on small rick-rack I sew straight down the middle. On slightly larger rick-rack and up, I will use a straight stitch, but either use a darning foot with feed dogs covered (or dropped, if you can drop them) or else will just ease the stitch line a bit to the left and right to help tack down the edges a little bit. It does tend to curl a bit with washing. I take my mini iron (or a regular iron) and press down the edges of the rick-rack because I don't like the curled look, but that's up to you.
I use a LOT of rick-rack on quilts and have never pre-washed it & haven't experienced any issue with it shrinking. It's synthetic fiber, so less prone to shrink than cotton anyways. My biggest issue was fraying until I learned that you can melt the raw edges with a match/lighter. No other issues.