Plastic mulch offers some benefits over organic mulch. The most obvious of these are its durability and uniform appearance. One of the drawbacks of plastic mulch is that it can, depending on the type, require a much steeper initial investment than organic mulch. But you can easily avoid that expense by creating your own plastic mulch.
Find suitable plastic sheets to work with. They should be at least 3 feet wide, 1 mm thick and opaque. Weeds have no trouble germinating under clear plastic. Black is the most common color, but anecdotal evidence suggests that plastic mulch that is the same color as the crop grown over it (red plastic for tomatoes or blue for blueberries) increases yield. Experimenting can't hurt.
Lay the plastic mulch so that it covers the entire planting area. You may want to secure it with a few well-placed rocks at this point to keep it from blowing away before Step 3.
Bury the ends of the plastic bags. Dig 3-inch deep trenches with your spade and bury the ends of each plastic bag 3 inches deep so it won't blow it away.
Cut holes in the plastic (roughly 6 inches in diameter) where you intend to plant your plants or seeds.