How to Attack From North/South in BJJ
The north/south position fits neatly in with side control attacks, but like all other forms of side control, the position requires some specialization. High level competitors like Jeff Monson and Marcelo Garcia were all but unstoppable with the classic choke from north/south, so we'll start there, but keep in mind that transitioning to and from the position from other forms of side control is at least half the battle.
Start the north/south choke by circling from 100 Kilos side control, grabbing your partner's belt with your right hand. Keep the belt grip as you slide into north/south, because your partner is likely to create strong defensive frames to prevent you from easily securing the choke. Use the belt to pull your chest forward, scraping their hands away from their neck. Now snake your left arm around and under their neck, securing the choke position. Use your biceps on one side to cut off the flow of blood, and use your ribs on the other side to close the triangle (remember, all chokes are like triangles, in that three sides are cut off when choking). In the video, I use a stacking method for making my bottom arm "taller" (closing the triangle tighter). Finally, squeeze by simply flexing your biceps. If your position is correct, the choke should be virtually effortless.
Choke to Kimura
One of my favorite transitions from the north/south choke leads straight to a dominant Kimura grip (the entire Kimura system is here). Start with the belt grip choke set up as previously described. When you're unable to get the choke, give your partner just enough of a nudge so that they can see a possible escape route by lifting them up and pushing them away. As they go to try to turn out at the opening, slide your trail arm through from behind, catching the Kimura grip. Once you have this position, you can easily transition to the back or to an armlock. If your opponent turtles, use this opportunity to set up a crucifix.
Transitioning around North/South
One very common and effective method for utilizing north/south is as a pass-through transition. Start by catching an underhook from knee on stomach (a classic spinning armbar set up), and then step over your partner's head. Here's where the north/south transition can really be your friend: sit down on your partner's head while you are squatting (use the tension of them wanting to hold on while you're trying to armbar them as an anchor grip, kind of like the Kimura grip). Just cross your rear leg (my left in the video) over and around your partner's hips, securing a very tight armbar finish position.
Brabo set up
Start with a strong hip-switch side control (reverse kesa gatame), constantly threatening both moving to the mount and the Kimura. The trick here is to get your partner to turn away from you, giving them just a glimmer of hope (one way to do this is by grabbing their pants at the knee and physically turning their hips away; many will see daylight and go for the escape). From here, there's a simple slip right into a brabo choke. Once again, the transition through north/south and around to the other side is key.
North/South or Modified Kesa?
North/South was one of the first pins I learned in judo, and it remains an effective holding position today, although I generally tend to transition to and from north/south rather than lurking from the pin the way I might stay in, say, reverse kesa. If you can properly integrate a little north/south, even if it's only transitioning into a submission, you're likely to see a huge increase in your side control finish percentage (and control time). As always, let me know how these techniques work for you!