If you store large volumes of polypropylene or polyethylene material, make sure to rotate the stock regularly since these materials are typically treated to promote ink adhesion, and the pretreatment decays over time. If it is old stock, check the surface energy. If you use coated papers for transfers, maintain them in the correct climate to ensure proper performance. Also keep an eye out for safety issues in your storage areas, such as untrained forklift operators. The ink storage and mixing area can be a source of nightmares.
Ink is the biggest potential variable in the process.
And avoiding ink waste begins with your supplier. As printers become more sophisticated, controlling the quality of incoming ink is vital. If you have to send an unsatisfactory batch back, it may do wonders to improve your supplier's own quality-control measures. When producing color swatches for testing ink color or density, make sure to emulate real production conditions as closely as possible. If you use a drawdown bar, make sure the ink thickness you produce is consistent with what you'll get during production.