The rules are what you just said above.
Slip pw unless you're decreasing - that's what a ssk is, so you sl kw for knits, pw for purls. A ssp is a little different, you have to sl the stitch kw or it won't lie flat on the other side.
That's really how I do all my slips, whether it's `right' or not. I slip them kw on the knit side, or if they're between k sts, and pw on the purl side. I don't slip at the beginning of a row, so I just ignore that part.