You put the prop on the balancer.

Make sure the prop is centered on the balancer ( twisting the inner support on the hub helps to do this... ).

The blade that goes down, is the heaviest.

Sand, or shave off a bit of material until you have the blades as level as possible.

I don't go as far as making them level with the ground, but if there is no tendancy to have one more than 10-15% out of level I consider that OK.