Like Drycreek said above, make sure the scope is level, then I like to apply just a bit of Blue Locktite & torque to whatever specs are indicated by the manufacturer, or based on the type of rings (aluminum vs steel).
Usually I'll boresight by removing the bolt & 'eyeballing' the center of the bore on some distinct point on a target (like the 90* corner of a target stand) & adjusting the reticle or dot on the same point. This is usually good enough to make sure the first round is on paper at 25-50 yds.
If its a 5.56 AR-style rifle, I'll use a 36yd zero.
Any other scoped rifle I'll use 100yds to zero, & collect muzzle velocity (MV) data while zeroing.
After getting a solid zero, remember to 'slip the rings' on the scope elevation/windage knobs to 'zero', so you can return to zero if making any adjustments later.
With a solid 100yd zero & MV (plus temperature / barometric pressure of when MV was collected, & ballistic coefficient / projectile weight), I can then run it thru a ballistic calculator to get a generic Drop Chart for whatever distances I plan to shoot.
Works good enough for me
