I was taught to start with water...then use a coffee can or some vessel to add plaster into the water until you see the mountain cone of plaster rise above the water a bit...then mix. ALso, if you tap your bucket hard against the floor, or hit it on the side a few times with a hammer, the air bubbles will rise to the top. ALso, keep your hand submerged while mixing so as not to stir in air.
Pour it when it is like thick cream.
Linda in Houston