Make sure you start with a mechanical zero.
Crank the elevation adjustment knob all the way to the bottom then count the click adjustments to all the way to the top, go back down half (or 2/3) that number. You typically don't need to adjust <down> as much with a 2-300 yd zero.
Do the same with the windage adjustment but adjust that back dead-on in the middle.
That should give you, prior to mounting, the most amount of adjustment in any direction. If the reticle starts off uncentered and is mounted hinky you may end up without room to adjust it. A good MZ should be achieved before zeroing any kind of sight, iron or optic.