There is no singular magic formula for creating a supersaturated solution of sugar in water. The best way would be to take 3 gallons of water and heat it up a bit higher than room temperature. Then add sugar and stir to dissolve it until no more sugar can dissolve in the solution (you will see solid sugar sitting in the bottom of the solution). Then pour the solution carefully into a new container to keep the undissolved sugar from pouring with the liquid. Finally, allow the sugar solution to cool to room temperature. You will then have a supersaturated solution of sugar water. Be careful though because any disturbance could cause the sugar to start to crystallize from solution. It also helps to use a container with a very smooth surface because imperfections in the surface help to induce crystallization.