For working in the round, any style (small circular, magic loop, dpns) I cast on one extra stitch. I work the first row flat (ribbing or plain or whatever), except for the last stitch. I set it up to join to work in the round, and then knit that last unworked stitch together with the first stitch of the new round. This helps tighten things up.
The other way that I do it is to cast on the extra stitch, work the entire first row flat. Then slip the first stitch of the next round knitwise, then pass the last stitch of the first row over the slipped stitch.
Both of these methods decrease away the extra stitch, so you’re back to the required number of stitches.
The advantage to working that first row flat is that you have more to look at when you’re making sure you don’t have a twist.