Here's a link to an earlier post that has internet sites on combined knitting including the NonaKnits one:
If you're doing 2x2 rib, you only need to change the first purl stitch to combined knitting. If you're doing 1x1 rib, change each purl stitch. Basically, you want to use combined knitting on the first purl stitch that follows a knit stitch in ribbing. This will help tighten up the loose knit stitch that precedes the combined purl stitch. I learned how to do this best from the NonaKnits link and watching Amy's KH videos on combined knitting which are under the knit and purl sections.
The above link to a previous post concerns only knitting in the round where there is no WS. If you're doing combined knitting for ribbing on straight needles, it's even easier because when you do the WS, you do the same exact thing as you did on the RS row. Only the very first row is different: on the first row you wrap the yarn clockwise for the first purl st the follows a knit stitch. The second row on, you add one more action to what you did on the first row: knit into the back loop of the twisted stitches (which were the purl stitches that you did clockwise on the previous row). It seems like a lot to remember, but after just a few rows, it will make sense. IMO it takes longer than regular ribbing, but is worth it if you have any prominent ribbing.
One more thing: when you get to the end of your ribbing, you'll need to quit wrapping your purl stitches clockwise and you'll need to correct the mount of your twisted stitches. If you have any kind of pattern on the first row after your ribbing, you'll need to make the last row of ribbing be correcting the mounts and not wrapping clockwise. If you have stockinette stitch, or something plain like it, on that first row after ribbing, you can correct the mounts and not wrap clockwise on the first stockinette stitch row.
I'm so wordy, aren't I?! Sorry!