Hey Marvin,
The basics are that the first three entries are Z, X, and Y. Y is Height, Z is longitudinal, and X is width...
Then, from there, find some dirt to taxi in, set up your FS to have 'aircraft reload' (perhaps use Control/Shift/R like us developers), so that you can continuously reload your plane to check its progress.
Next, taxi, study the dust fly, and reset your contact points.
Some people, like famous guru Milton Shupe, use a Nav Light in the same location to track the point of the contact location, moving it until its right where it should be. Then delete the light when you are done, having moved the Z, X, Y locations from the light locations for each contact point.
For visibility on 'height', use a hard runway, such as Seattle/Tacoma, and set time of day for dusk with the sun still partially up. This creates a brilliant side shadow that will show just how high your tires are from the ground, touching, hovering, etc. I always sink them down in the pavement an inch for a bit of realism.
Hope that helps.
Bill