Two good variations for knife defense are sitting on your behind with your legs stretched in front of you and sitting on the shins and knees with the behind high in the air. You stay or sway a bit in these two starting positions and your partner comes at you with a stab or a slash and you first let it come in, feel the direction of the knife and the body of the partner and relax and move with it. Once you are on the go add a direction of your own and work on moving your body out of the way of his knife and body, work to keep the knife engaged and in your awareness so you avoid having a struggle over a knife in tensed up hands (you will be cut badly and you will lose your awareness to movement and the view around you) or getting the knife away and getting a knee or fist well into your face or neck, Work to keep your eyes free from focusing on one point, keep breathing and feel your shoulders and hips work freely. The work on the knees allows you to feel how it is when the hips are tense in the start (walking in snow/mud for example) and will allow you to discover new ways you can move.
After you have done this a few times with letting the knife touch and moving with it start moving when you start feeling uncomfortable or threatened. Don’t worry about looking cool, the cool kids don’t know they are cool 🙂
A preparation drill for this work is to tense up a body part and as it is tensed up you keep breathing and relaxing and moving the hips and shoulders seperatly. Don’t forget to also tense up one hip and relax and move the other and the same for the shoulder.
Relax, Breathe, move, Live.