I could never get it by paying attention to Paul's elbow, but after watching his right foot it's slowly becoming more natural to me. This tutorial helped a bunch, thanks man!
when you see the blue sparks that means you timed it perfectly (that's called just frames) as a result you do +2 extra damage if there's no sparks that means the timing was a fraction early/late or in video game term a few frames too early/late and if the third hit doesn't come out at all...you get the gist