From my friend Richard Marsden from a HEMA discussion on how to teach folks how to avoid double kills. I think it would be very good as a cross-discipline tool to help folks of all skill levels.
"Hello, I teach lots of students, some quite young. Here are my experiences.
I set up a culture right away of discouraging double-kills. One way we do this is in slow drills at the start called robot-drills in longsword.
Each student picks a guard (Fiore has lots) then on the count of three they get to make one movement at the same rate of speed. We count down again and again till there is a victor. In this slow, methodical training method we rarely get double-kills. Students can see what's going on, they understand the 'game' and they don't consciously decide, "Yeah, hell with it- double kill time."
After we get students used to robot drills we speed up and eventually move into sparring. The robot drills pay off at this point as students have an understanding of how to play to survive- not just win.
Another technique is to really drill the moving off the line in longsword so attacks and defenses aren't directly at the opponent, but use a little movement here and there to be safe.
In rapier, longsword and other systems, we show plays and how they work. When we ask students to find counters, we discourage any counters that will get them hit.
These little techniques have paid off fairly well in our group so far."