Not trashing anyone, but I am a little anal when it comes to my zeroing so I do not try to do it in 2 or three shots ever, unless I am verifying a previously zeroed rifle or changing ammo, so don't be afraid to burn a little bit of powder.
Yes there are a variety of practices out there for sure. My method is to start from the bench at 25 yds (you can start at longer ranges too). I set up a scoped rifle in a rest, remove the bolt, if it has one, and look through the bore to find the center of the bull, adjust the rifle in the rest until the bore centers on the bull and re-secure the rifle in the rest. I then look through the scope to see where the cross hairs are and dial the cross hairs to the center of the bull. I will then fire a shot to see if I am where I want to be and it is usually pretty close. I will dial in for a few more shots and then move out to 100yds. It will likely be shooting a little high, how high depends on a couple of things, there are charts that will tell you how high you need to hit the bull at 100 to be zeroed at say 200, 300 and so forth. The longer ranges can't be verified fully unless you actually shoot those of course and I don't because I don't take shots beyond 200 with anything anyway.
Sighting in for open sights is a similar process with a lever action, single shot, etc., except you strap the gun down and adjust the rest to line the sights up on the bull, I start at 25yds and make windage/elevation adjustments as needed and then move out to 50 or 100, depending on the gun.
Once all of that is done I use a process that I read many years ago that Gunny Hathcock was reputed to have used, and it takes a little time, works for me. When I hunt I am going to be taking my first shot from a cold clean barrel, or a barrel that has had a "fouling" shot. So I go out and shoot the target, one round only. Then I go back, clean the gun, and wait until the barrel returns to its "cold" state. Sometimes you can do that more than once a day, sometimes not, it depends on the temperature outside. After the gun is back to its original state I go out and shoot one round at the same target, same rest, same hold, just like I did the first time. I repeat this 3-5 times and I will then know where that particular gun will shoot from a cold, clean barrel on the first shot.
That process is done to see what the GUN will do with as little human element input as possible, I will be holding and/or supporting differently in the field so it is a good idea to practice your hold and/or support beforehand so you can then see what YOU will do with the gun in the field.
Probably leaving a few things out but that is my general practice.