Columns come in many different shapes and sizes. Their proportion and scale should relate to the style of the house and should not be spaced too widely apart resulting in unnatural looking beam spans. The cap should always project past the face of the porch beam while the base of the column shaft should line up with the pier face below. Due to the taper of most columns, the outside face of the porch beam will not line up vertically with the edge of the deck below...don't worry, it will make sense when you see it on paper.
More information on columns to come in future posts...