Iso pre-fatigue is one of my favorite intensification methods. It helps stimulate growth, but I like it even more as a way to improve the mind-muscle connection.
It's fairly straightforward: You start each set with an isometric hold at a key position in the movement. Use the position where you can feel the most tension in the target muscle. Hold the isometric in the mid-range position for 10-60 seconds, then do as many reps as you can.
The hold should be anywhere between 10 and 30 seconds depending on how strong you are. You could go up to 60 seconds, but most people should try a 10-30 second hold with maximum tension. In the video Paul is using the 60-second version because he's a pro football player who squats over 500 pounds, but even bodyweight alone crushes him!
And here's the secret, try to feel the same tension as you did during the hold. If you can get more than 12 reps, lengthen the hold or slow down your reps.
Make it as demanding as you can! This means creating as much tension as possible. Try to "screw your feet into the floor" by attempting to externally rotate them, or "press the floor with the toes" and "tense the abs as if you were going to get punched in the stomach."
These actions will not only create more muscle fiber recruitment, they'll also develop your capacity to contract and feel key muscles. That way, when you get back to lifting weights, these muscles will respond a lot better.