If you're making a sweater and the ribbing has open edges, you are evidently not knitting in the round, but back and forth intending to seam the sides. That being the case you don't need to be that concerned about a super neat edge. A normal, carefully done rib will work just fine. Some people swear by slipping the first stitch even when they seam, but I never do and at the class on finishing for knits that I took the lady advised against slipping stitches.
I'd just rib normally and after the first stitch of each row pull it nice an tight before doing the next stitch. Works for me.
About the slipping. When I do use it, like for a scarf, I like to slip the first stitch purlwise with the yarn in front. Along with that I knit the last stitch of each row. Keep all the edge stitches quite snug.