What is a Slip Stitch?
A slipped stitch is a stitch that is moved from your left needle to your right needle without wrapping the yarn to create a new knit stitch above it.
How to Slip a Stitch
If your pattern doesn’t specify which way to slip the stitch, slip it “as if to purl” or “purlwise.” This means you insert your needle from back to front and from right to left.
To slip a stitch, insert the right needle into the stitch on the left needle (from the back to the front), then slide it off the left needle, transferring it onto the right needle.
Where Should the Working Yarn Be?
If the pattern doesn’t say specifically, then leave your yarn where it is when you slip the stitch. In general, if the horizontal strand isn’t an intensional decorative effect on the front side of the fabric, then slip the stitch with the yarn held on the wrong side of the fabric.
(H/T Margaret Radcliff – The Knitting Answer Book).