You start with the depth and size of the holes. For a good strong fence you want 30 - 35% of the pole in the ground with a minimum of a foot and a half under the dirt. You want to make your hole at least five times the diameter of your pole (for normal fencing). Pour concrete in the hole with the pole in the middle but do not fill the hole all the way up, leave about six inches for dirt so grass can grow. Anyway, there ya go.
That also works really well for stronger cinder brick walls also. Hide the poles in the centers.