The easiest way to remember a yarn over
The way you wrap the yarn around the needle for a yarn over (YO) is determined by the stitch that will follow it, and my favorite way to do a yarn over is to look at the stitch that will follow the YO (in this case it is a Purl stitch) and then i PRETEND to work the following stitch without actually inserting the needle into the stitch. So, if the stitch that follows the YO is a purl stitch, then simply bring your yarn to the front (as you normally would to work a purl stitch), insert the needle into an imaginary Purl stitch ( you dont have to do anything with the needle, i just find this makes it easier when demonstrating to people) and then wrap the yarn around the needle to work this "imaginary" stitch, then hold the YO on the needle with your finger and work the purl stitch that follows the YO. A YO before a knit stitch is the same way: bring the yarn to the back, insert the needle into an imaginary stitch, wrap the yarn for a knit stitch, and then hold the YO on the needle with your finger while you work the following knit stitch. I hope you can understand, it's so easy to show people, but it's hard to make clear without showing you.