This wonderful cast-on produces a picot edge to ribbing. If you care about the fine details of your knitting, it's worth learning. And it's not that hard, because it builds on the long-tail cast-on you (should) already know. (See this blog's post for April 7, 2011, The Long-Tail Double-Edge Cast-On.)
This cast-on consumes about the same amount of loose-edge yarn as the long-tail, so measure roughly 12 inches for every 20 stitches. (I hold the leading edge in my left hand and run the yarn about 4/5 of the way to the crook in my elbow: that gets me about 20 stitches for each such pull.)
Now make a slip knot.
Make a tent with your left thumb and left forefinger, just as with the Long-Tail.
At this point the Long-Tail takes the tip of the needle up through the hole created by your left thumb. Hold that thought; we'll get to it in a minute. But first, for the Picot Cast-On, you're going to bring the needle tip under the left wall of the tent
and then you're going to snag the right wall of the tent, making a simple wrap on the needle,
and you're going to drag that wrap with you as you bring the needle tip up through the hole your thumb has made (now it's looking like the Long-Tail) . . .
and now you're going to grab the tent's right wall and pull it through the hole . . .
. . . and then you're going to release your thumb and snug the stitch up on the needle. Note that you now have three stitches on the needle: the slip knot is stitch #1, the wrap is stitch #2, and what you just pulled through the thumb hole is stitch #3.
Continue in this manner, adding two stitches with each set (the wrap and the drag-up-through-the-hole).
This produces an odd number of stitches, so if you're going to be doing k1, p1 in rounds, you'll need to add one more stitch. Cast on that one last stitch in the simple loop manner.
The dynamics of this cast-on remind me of the wrap-and-stitch dynamics of the Moebius cast-on, or the Provisional cast-on. In each case there's a wrap first, and then a stitch; both become stitches when they're ultimately knitted.