From a tree stand a quartering away shot is the most productive but a broadside is pretty good too. You want your arrow to go through the chest cavity and hit the opposite shoulder.
...and like Derik said, calm down, focus on the "spot" that the arrow WILL hit...and it will. Don't look at the whole deer. Pick that spot just behind the shoulder that is in line with the off side shoulder or leg. That will put that arrow through the boiler room.
Aim small, miss small!