Before the application of any emulsion to the mesh you have to make sure the screen is properly degreased. Is this step necessary? The answer is yes, especially if you have a brand new screen. Degreasing the screen clears out any oils, dirt, dust, etc that make their way to the surface of the mesh and can cause pinholes or premature screen breakdown. Just do it. Seriously.
You can actually use Mr. Clean as your degreasing agent or and industrial strength degreaser. Do not use household scouring powder like Comet as it will ruin your screens quickly.
Simply apply the degreasing agent onto your screen and scrub with a nylon or screen brush. Rinse the screen off with water once you have degreased both sides of the screen.