I'd suspect the single biggest issue I see with scope adjustment is improperly adjusting reticle focus BEFORE you do anything else relative to parallax [if there's an adjustment].
You must do this while looking at a neutral background, like the sky. You must also look through the scope only breifly while ckecking reticle, if you look for several seconds your eye will compensate now and then give you eye strain when shooting for a while. you need to get close on the ring and when close look through the scope and made small adjustments until you can look away for a few seconds and look back and see if the reticle is IMMEDIATLY in focus. go back and forth a few times until you get there. The higher the power the smaller the final adjustents should be but remember when set you want the reticle instantly sharp. once that is set any parallax adjustment then follows.
Remember, if your over 50 this is likely going to need readjustment probably every 12-18 months since everybodies eyes change.