Before you shoot make the scope you are using is good for the rifle (don't get a long range scope for a 20-2). Also make sure you are using the same powder load, shot/bullet/ cartridge, and primer as you would for hunting. Different loads yield different groupings

Here is the method I always use.
First you need a consistent grouping, the best way to achieve this is to fire at a directional bulls-eye. after about 5 shots check your grouping, then move your scope's crosshairs to the THE GROUPING, not the bull-eye.
rinse and repeat for added adjustments
I go hunting at least 3 times a year, this method is always the best as it uses the least amount of ammunition. You can use the same method for archery.

Yeah Kargo mentioned the part that I forgot to say, how to actually adjust it. And make sure that you get fairly strong groups to go off of.

Why don't you no-scope? Scrub.

In addition, make sure your optic is zeroed for the ranges you are likely to be shooting at. For example, 200 meters is a good zero range for 5.56 x 45mm NATO rifles.

If you want to be really high speed, take a look at the ballistic data for the weapon and ammunition you are using and pick the best range to zero. For example, on my recently-purchased Mini-14, I have an EOTech zeroed for 200 meters, because I hold down a little bit on anything shorter than 200 meters, and hold up on anything further than 200 meters. The first step to choosing a good zero is to know your weapon and know the most likely application of your weapon.

Zeroing at anything less than 100 meters is unwise, because on most modern rifle calibers, the trajectory is quite flat at short range and a 200-meter zero will still put you on target at close range. As a rule of thumb, I prefer to zero at about 1/3rd of the maximum effective range of the weapon.

Thanks Guys!