Ribbing is a problem for many people. Not the technique itself because it's just a series of knits and purls, but that first purl after a knit segment tends to be loose and if you're like me it drives you crazy. nonaKnits figured out how to make improved ribbing when knitting flat, but ribbing in the round still vexed me. Her method doesn't provide good results (IMO) when knitting in the round so I searched Ravelry and then internet in general and discovered that others had problems too, but no one had definitive answers. So I played around with knitting in the back of the first purl, wrapping the yarn clockwise instead of counter clockwise and finally settled on a method that IMO looks great.

Purl into the first purl stitch after knits like you always do EXCEPT wrap the yarn under or clockwise instead of over the top. This twists the purl stitch. On any other purls following do them normally. Continue this method as long as you're ribbing.

A warning: Because that first purl is twisted this method is not reversible because the knit on the opposite side looks funny. So use it for ribbing that will in the round with the RS facing out. So no flipped brims.. ;)