What are the recommended installation steps for a level plywood subfloor?

The recommended installation steps for a level plywood subfloor are as follows:

1. Ensure the existing floor is clean and free of debris.
2. Measure and cut the plywood sheets to fit the room.
3. Lay down a moisture barrier if needed.
4. Start in one corner and secure the plywood sheets with screws or nails every 6 inches along the edges and every 8 inches in the field.
5. Stagger the seams of the plywood sheets for added strength.
6. Use a level to check for any uneven spots and sand or shim as needed.
7. Finish by sealing the seams with wood filler and sanding the entire surface for a smooth finish.