I've gained some insights lately, specifically in longsword play that I thought I'd share. These all came from self-diagnosis, which is crucial for learning and is best done during your practice sessions when you can direct your own exercises.
First, credit goes to Sean Hayes, Devon and Roland for their individual contributions and to me for my own.
So...
1. If your feet slide your step should be larger
What I mean is that if, using legitimate footwork, your feet want to advance slightly after a cut, you probably need to set your pace to where your foot is ending up.
2. Use both arms in a cut
It's easy to throw a one-handed cut - using your high hand - while your lower hand hangs around for the ride. Your cuts will be much more effective if both hands are employed: the low hand pulls while the high hand pushes.
3. The entirety of your lower hand should grip the sword
This one may depend on what sword you're using and the size of your hand. But my technique improved greatly when I ensured that my whole hand (pinky included!) was gripping the handle.
4. Bring your weapon around your shoulder; not along it
I didn't realize that I was doing this (with a dull sword) until I had to cut a lot fendente cuts; drawing the sword along your shoulder leads to a very sore shoulder. Pain and discomfort are great teachers (more on this in a later post).
Instead, pivot the weapon around your shoulder. Your cut will be much more effective (and your shoulder will hurt less). This leads nicely into...
5. I'm not telling you 5.
This one's too good and I'm keeping it to myself.