One thing I do with G-style guitars is to place the bridge on some lollipop sticks (to simulate it sitting correctly in the bridge posts). Then with the neck in place I run a long straight rule down the center of the fretboard (ruler on its edge) and over the bridge. You should be on track if the bottom edge of the rule touches the top of the bridge. If there is a large gap between the bottom edge of the rule and the top of the bridge some other factors may need to be considered...