I zero scopes for whitetail hunting at 200 yards. I've got a few nice scopes with ballistic / long range reticles and others that are plain old standard reticles albeit in high quality scopes. The most powerful scope I have on a deer rifle is 4X12, the rest are 3X9. Varmint rifles are higher 5X20.
What really gets the job done for me though is my willingness to use and access to a rifle range. If I don't get out and shoot 2 or 3 times a week I have shooters withdrawal. I hunt varmints, that is also a great way to hone your skills (once again very fortunate to access). Time is of the essence when hunting, being prepared to me is a culmination of things that include flexibility. Although I can shoot pretty well off hand short of squirrels I never do. Shooting sticks, bi-pods (my favorite), knees, trees, rocks, backpacks all make good rests. Some kind of a rest is better than no rest at all.
Study your bullet drop and windage charts, practice as much as you can. #1 thing is to think safety, knowing what's beyond your intended target (never skyline) is paramount to me. The ability to not take the shot is what makes an ethical hunter IMO.