For us, 300 yards is not considered long range. But, know your rifle; know your ammunition; use a rifle capable of a clean kill at longer ranges; and be at least adequate in estimating range. A good shortcut (assuming you hunt where long shooting is routine) is to sight your rifle between 4.5" and 6" high at 100 yards. You hold low on hair to 250 yards and high on hair to 400 yards. Read the following article to follow the logic.
http://www.kifaru.net/posimag.htm
P.S. - Great Question.
P.S.S. - Practive, practice, practice.