You will need a bucket, scale and mixing equipment. Mixing could be accomplished through basic hand mixing with a large spoon, but mechanical mixing is preferred. An electric drill with a cage mixer head attached is good for small batches.
The first step involves measuring and adding enough water to the bucket to achieve the desired consistency. You then need to weigh out enough gypsum plaster to meet the proper ratio for the selected water volume. Sift the plaster into the bucket of water and allow the plaster to soak for 1 to 2 minutes. Follow this immediately with mixing, generally for 1 to 2 minutes based on product.
NOTE: If mixing by hand, use vigorous stirring action. After mixing and pouring the gypsum slurry, make sure to clean all tools and the mixing vessel before the plaster hardens.
For more detail on mixing, see USG publication IG503, Plaster Mixing Procedures.