Tell them to listen to the beep (assuming the newer units still beep).  When the laser is taking too long to get feedback the beep takes longer to happen. The longer it takes to hear the beep, the less I trust the measurement.

Also, they will need to learn when to shoot something and when to just draw it.  Many times it makes no sense to try and shoot a raised bar or a 24'' piece beside a stove.

Mory,
One thing they will need to adjust to, is they need to think in terms of 2D, unlike the photo stuff. You can raise the device, for instance, to continue the same digital template (for instance if you wish to hit a wall above and behind a splash) you are merely continuing the same template with a readjustment.