Easiest way to use JMS is this:
Picture your boxes to look like this:
4 7
2 5 8
1 3 6 9
Then follow the normal GMS rule (using the diagram above), if you notice you don't have to jump as much. I've seen this before, and heard that "all the pro's use JMS" because it's faster, I guess because you can walk to each number it makes it a little easier. It's a cleaver idea non-the-less, and easy to use if you imagine your boxes to look like the digram above. I don't mean to reiterate anything anyone else has said. I know at first I was like what the hell is this, and all I could find was info on GMS until a friend explained it to me.