Here's a hint that has helped me in my jodo a good bit. Mark up your practice jo and bokken with a black Sharpie so that you will have significant reference marks. I thought about using marking tape so that I'd have a tactile as well as visual reference, but I figured the tape would rapidly wear off, leaving the jo gummy. Here's how I marked mine:
For the bokken, first find the center of mass of the weapon by balancing it on one finger. Place a mark on the flat back edge right at the center of mass. It doesn't have to be conspicuous to others, but it should be highly visible to the swordsman holding the bokken. Then hold the tip end of the bokken in one closed fist and make a second mark on the back edge that is one palm-width from the tip. This marks the cutting surface (the last 3 inches) as well as marking the point to cross sword and jo to measure ma-ai. The center-of mass mark serves mostly as a reference point for your subconscious to make note of relative positions every time the jo and sword meet during a technique.
For the jo, make a mark at the center of mass just as above. Then hold the jo in a proper honte grip and make a mark at the point that your front index finger and thumb rest on the jo. Do this on both ends. Finally, make a mark one palm-width from the end of the jo on both ends.
These marks will be valuable references during kihon in getting your grips precisely correct, they will help you develop a more precise understanding of ma-ai distance, and they will serve as positional references for all the techniques.