Good ventilation is the most important factor in having dry wood. It helps to dry the wood by speeding up evaporation. If you have the space, you might want to employ a trick used by old timers. They stacked their wood in long thin rows spaced apart, and at right angles to the prevailing winds to ensure good ventilation. Covering the wood and keeping it off the ground are important because these practices keep the wood away from moisture.
Wood acts very much like a sponge.
If it is exposed to rain, snow or moisture in the ground, it will soak this water right up, putting to naught all your efforts to dry it out. This will trap the moisture in the pile and the wood will not dry. If you can, make a simple wood frame to raise the plastic cover a few feet above the wood. The ultimate drying place is an open sided shed. Use 2 x 4's, poles, or pallets or some other method to keep your wood off the ground.